diff --git a/runelite-client/src/main/java/net/runelite/client/RuneLite.java b/runelite-client/src/main/java/net/runelite/client/RuneLite.java
index e6292b4087..d2bf8e14df 100644
--- a/runelite-client/src/main/java/net/runelite/client/RuneLite.java
+++ b/runelite-client/src/main/java/net/runelite/client/RuneLite.java
@@ -85,6 +85,7 @@ import net.runelite.client.ui.overlay.arrow.ArrowWorldOverlay;
 import net.runelite.client.ui.overlay.infobox.InfoBoxOverlay;
 import net.runelite.client.ui.overlay.tooltip.TooltipOverlay;
 import net.runelite.client.ui.overlay.worldmap.WorldMapOverlay;
+import net.runelite.client.util.AppLock;
 import net.runelite.client.util.WorldUtil;
 import net.runelite.client.ws.PartyService;
 import net.runelite.http.api.worlds.World;
@@ -201,6 +202,9 @@ public class RuneLite
 	@Inject
 	private Scheduler scheduler;
 
+	@Inject
+	private AppLock appLock;
+
 	public static void main(String[] args) throws Exception
 	{
 		Locale.setDefault(Locale.ENGLISH);
@@ -368,9 +372,11 @@ public class RuneLite
 		externalPluginManager.startExternalUpdateManager();
 		externalPluginManager.startExternalPluginManager();
 
-
-		RuneLiteSplashScreen.stage(.59, "Updating external plugins");
-		externalPluginManager.update();
+		if (appLock.lock(this.getClass().getName()))
+		{
+			RuneLiteSplashScreen.stage(.59, "Updating external plugins");
+			externalPluginManager.update();
+		}
 
 		// Load the plugins, but does not start them yet.
 		// This will initialize configuration
@@ -490,5 +496,6 @@ public class RuneLite
 		configManager.sendConfig();
 		clientSessionManager.shutdown();
 		discordService.close();
+		appLock.release();
 	}
 }
diff --git a/runelite-client/src/main/java/net/runelite/client/plugins/ExternalPluginManager.java b/runelite-client/src/main/java/net/runelite/client/plugins/ExternalPluginManager.java
index eec6d2bb2e..e9c3afad37 100644
--- a/runelite-client/src/main/java/net/runelite/client/plugins/ExternalPluginManager.java
+++ b/runelite-client/src/main/java/net/runelite/client/plugins/ExternalPluginManager.java
@@ -77,7 +77,7 @@ class ExternalPluginManager
 {
 	public static ArrayList<ClassLoader> pluginClassLoaders = new ArrayList<>();
 	private final PluginManager runelitePluginManager;
-	private final org.pf4j.PluginManager externalPluginManager;
+	private org.pf4j.PluginManager externalPluginManager;
 	@Getter(AccessLevel.PUBLIC)
 	private final List<UpdateRepository> repositories = new ArrayList<>();
 	private final OpenOSRSConfig openOSRSConfig;
@@ -104,6 +104,11 @@ class ExternalPluginManager
 		//noinspection ResultOfMethodCallIgnored
 		EXTERNALPLUGIN_DIR.mkdirs();
 
+		initPluginManager();
+	}
+
+	private void initPluginManager()
+	{
 		boolean debug = RuneLiteProperties.getLauncherVersion() == null && RuneLiteProperties.getPluginPath() != null;
 
 		this.externalPluginManager = new DefaultPluginManager(debug ? Paths.get(RuneLiteProperties.getPluginPath() + File.separator + "release") : EXTERNALPLUGIN_DIR.toPath())
@@ -241,6 +246,8 @@ class ExternalPluginManager
 	{
 		try
 		{
+			repositories.clear();
+
 			for (String keyval : openOSRSConfig.getExternalRepositories().split(";"))
 			{
 				String id = keyval.substring(0, keyval.lastIndexOf(":https"));
@@ -474,6 +481,21 @@ class ExternalPluginManager
 
 		for (PluginWrapper plugin : startedPlugins)
 		{
+			boolean depsLoaded = true;
+			for (PluginDependency dependency : plugin.getDescriptor().getDependencies())
+			{
+				if (startedPlugins.stream().noneMatch(pl -> pl.getPluginId().equals(dependency.getPluginId())))
+				{
+					depsLoaded = false;
+				}
+			}
+
+			if (!depsLoaded)
+			{
+				// This should never happen but can crash the client
+				continue;
+			}
+
 			scannedPlugins.addAll(loadPlugin(plugin.getPluginId()));
 		}
 
@@ -673,6 +695,7 @@ class ExternalPluginManager
 
 	public void update()
 	{
+		boolean error = false;
 		if (updateManager.hasUpdates())
 		{
 			List<PluginInfo> updates = updateManager.getUpdates();
@@ -687,14 +710,24 @@ class ExternalPluginManager
 					if (!updated)
 					{
 						log.warn("Cannot update plugin '{}'", plugin.id);
+						error = true;
 					}
 				}
 				catch (PluginRuntimeException ex)
 				{
 					log.warn("Cannot update plugin '{}', the user probably has another client open", plugin.id);
+					error = true;
+					break;
 				}
 			}
 		}
+
+		if (error)
+		{
+			initPluginManager();
+			startExternalUpdateManager();
+			startExternalPluginManager();
+		}
 	}
 
 	public Set<String> getDependencies()
diff --git a/runelite-client/src/main/java/net/runelite/client/util/AppLock.java b/runelite-client/src/main/java/net/runelite/client/util/AppLock.java
new file mode 100644
index 0000000000..aca0832439
--- /dev/null
+++ b/runelite-client/src/main/java/net/runelite/client/util/AppLock.java
@@ -0,0 +1,64 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 by rumatoest at github.com
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package net.runelite.client.util;
+
+/**
+ * The Class AppLock.
+ *
+ * @author Vladislav Zablotsky
+ */
+public class AppLock
+{
+
+	private static CrossLock lockInstance;
+
+	/**
+	 * Set lock for application instance.
+	 * Method must be run only one time at application start.
+	 *
+	 * @param lockId Unique lock identifiers
+	 * @return true if succeeded
+	 */
+	public synchronized boolean lock(String lockId)
+	{
+		if (lockInstance == null)
+		{
+			lockInstance = new CrossLock("application_" + lockId);
+		}
+		return lockInstance.lock();
+	}
+
+	/**
+	 * Trying to release application lock.
+	 * Thus another application instances will be able to use lock with current ID.
+	 */
+	public synchronized void release()
+	{
+		if (lockInstance != null)
+		{
+			lockInstance.clear();
+		}
+		lockInstance = null;
+	}
+}
\ No newline at end of file
diff --git a/runelite-client/src/main/java/net/runelite/client/util/CrossLock.java b/runelite-client/src/main/java/net/runelite/client/util/CrossLock.java
new file mode 100644
index 0000000000..5db7a63432
--- /dev/null
+++ b/runelite-client/src/main/java/net/runelite/client/util/CrossLock.java
@@ -0,0 +1,228 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 by rumatoest at github.com
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package net.runelite.client.util;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.nio.channels.FileChannel;
+import java.nio.channels.FileLock;
+import java.nio.channels.OverlappingFileLockException;
+import java.util.HashMap;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import static net.runelite.client.RuneLite.RUNELITE_DIR;
+
+/**
+ * Universal cross application instances locker.
+ * Allow you to create simple lock like object which can be used for
+ * different application instances. Basic idea is simple - just a simple file lock.
+ * <br />
+ * All you need is to define unique key for each lock type.
+ *
+ * @author Vladislav Zablotsky
+ */
+public class CrossLock
+{
+
+	private static final HashMap<String, CrossLock> locks = new HashMap<>();
+
+	private final String id;
+
+	private final File fileToLock;
+
+	private FileOutputStream fileStream;
+
+	private FileChannel fileStreamChannel;
+
+	private FileLock lockOnFile;
+
+	/**
+	 * Will create or retrieve lock instance.
+	 * Each lock id is unique among all you instances,
+	 * thus only one instance can acquire lock for this id.
+	 *
+	 * @param lockId Unique lock identifier
+	 * @return Not null
+	 */
+	public static CrossLock get(String lockId)
+	{
+		if (locks.containsKey(lockId))
+		{
+			return locks.get(lockId);
+		}
+		else
+		{
+			synchronized (CrossLock.class)
+			{
+				if (locks.containsKey(lockId))
+				{
+					return locks.get(lockId);
+				}
+				else
+				{
+					CrossLock cl = new CrossLock(lockId);
+					locks.put(lockId, cl);
+					return cl;
+				}
+			}
+		}
+	}
+
+	/**
+	 * Will remove lock object for specific id and release lock if any.
+	 *
+	 * @param lockId Unique lock identifier
+	 */
+	public static void remove(String lockId)
+	{
+		if (locks.containsKey(lockId))
+		{
+			CrossLock lock = null;
+			synchronized (CrossLock.class)
+			{
+				if (locks.containsKey(lockId))
+				{
+					lock = locks.remove(lockId);
+				}
+			}
+			if (lock != null)
+			{
+				lock.release();
+			}
+		}
+	}
+
+	CrossLock(String lockId)
+	{
+		this.id = lockId;
+		fileToLock = new File(RUNELITE_DIR, lockId + ".app_lock");
+	}
+
+	/**
+	 * Return lock instance identifier.
+	 */
+	public String id()
+	{
+		return this.id;
+	}
+
+	/**
+	 * Activate lock.
+	 * Note! This is only cross application (cross instances) lock. It will not work
+	 * as lock inside single application instance.
+	 *
+	 * @return true if lock was acquire or false
+	 */
+	public synchronized boolean lock()
+	{
+		if (lockOnFile != null && lockOnFile.isValid())
+		{
+			return true;
+		}
+		else
+		{
+			release();
+		}
+
+		String lockContent = "#Java AppLock Object\n#Locked by key: " + id() + "\r\n";
+		try
+		{
+			if (fileToLock.exists())
+			{
+				fileToLock.createNewFile();
+			}
+			fileStream = new FileOutputStream(fileToLock);
+			fileStreamChannel = fileStream.getChannel();
+			lockOnFile = fileStreamChannel.tryLock();
+			if (lockOnFile != null)
+			{
+				fileStream.write(lockContent.getBytes());
+			}
+		}
+		catch (Exception ex)
+		{
+			if (!(ex instanceof OverlappingFileLockException))
+			{
+				Logger.getLogger(AppLock.class.getName()).log(Level.WARNING,
+					"Can not get application lock for id=" + id() + "\n" + ex.getMessage(), ex);
+			}
+			return false;
+		}
+
+		return lockOnFile != null;
+	}
+
+	/**
+	 * Release lock associated with this object.
+	 */
+	public synchronized void release()
+	{
+		try
+		{
+			if (lockOnFile != null && lockOnFile.isValid())
+			{
+				lockOnFile.release();
+			}
+			lockOnFile = null;
+
+			if (fileStream != null)
+			{
+				fileStream.close();
+				fileStream = null;
+			}
+
+			if (fileStreamChannel != null && fileStreamChannel.isOpen())
+			{
+				fileStreamChannel.close();
+			}
+			fileStreamChannel = null;
+		}
+		catch (IOException ex)
+		{
+			Logger.getLogger(AppLock.class.getName()).log(Level.WARNING,
+				"Can not get application lock for id=" + id() + "\n" + ex.getMessage(), ex);
+		}
+	}
+
+	/**
+	 * Release lock and remove lock file.
+	 */
+	public synchronized void clear()
+	{
+		release();
+		if (fileToLock.exists())
+		{
+			fileToLock.delete();
+		}
+	}
+
+	@Override
+	protected void finalize() throws Throwable
+	{
+		this.clear();
+		super.finalize();
+	}
+
+}
\ No newline at end of file