Created Unassigned: ToolkitScriptManagerHelper.GetAssembly null exception [27519]

Please see exception as follows:

例外狀況資訊:
例外狀況型別: System.NullReferenceException
例外狀況訊息: Object reference not set to an instance of an object.

執行緒資訊:
執行緒 ID: 6
正在模擬: False
堆疊追蹤: 於 System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
於 AjaxControlToolkit.ToolkitScriptManagerHelper.GetAssembly(String name)
於 AjaxControlToolkit.ToolkitScriptManagerCombiner.IsScriptCombinable(ScriptEntry scriptEntry)
於 AjaxControlToolkit.ToolkitScriptManagerCombiner.WriteScripts(List`1 scriptEntries, TextWriter outputWriter)
於 AjaxControlToolkit.ToolkitScriptManagerCombiner.GetCombinedScriptContent(HttpContextBase context, String[] bundles)
於 AjaxControlToolkit.ToolkitScriptManagerCombiner.GetCombinedScriptContentHash(HttpContextBase context, String[] bundles)
於 AjaxControlToolkit.ToolkitScriptManager.OnLoad(EventArgs e)
於 System.Web.UI.Control.LoadRecursive()
於 System.Web.UI.Control.LoadRecursive()
於 System.Web.UI.Control.LoadRecursive()
於 System.Web.UI.Control.LoadRecursive()
於 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)