My site application pool keeps on crashing from time to time

I get this error and then "Service not Available" and I have NO idea how to solve it, Please HELP
[ArgumentException: An item with the same key has already been added.] System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) +14493519 AjaxControlToolkit.ToolkitScriptManagerHelper.GetAssembly(String name) in f:\TeamCity\buildAgent\work\80acd78aa4c25314\Server\AjaxControlToolkit\ToolkitScriptManager\ToolkitScriptManagerHelper.cs:18 AjaxControlToolkit.ToolkitScriptManagerCombiner.IsScriptCombinable(ScriptEntry scriptEntry, Boolean enableCdn) in f:\TeamCity\buildAgent\work\80acd78aa4c25314\Server\AjaxControlToolkit\ToolkitScriptManager\ToolkitScriptManagerCombiner.cs:411 AjaxControlToolkit.ToolkitScriptManagerCombiner.WriteScripts(List`1 scriptEntries, TextWriter outputWriter, Boolean enableCdn) in f:\TeamCity\buildAgent\work\80acd78aa4c25314\Server\AjaxControlToolkit\ToolkitScriptManager\ToolkitScriptManagerCombiner. ...