Created Unassigned: Error - Collection was modified; enumeration operation may not execute. [27516]

There is discussion about this error @
http://forums.asp.net/p/1931886/5501172.aspx?p=True&t=635139958730585976&pagenum=1


StackTrace at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
at System.Collections.Generic.List`1.Enumerator.MoveNextRare()
at System.Collections.Generic.List`1.Enumerator.MoveNext()
at System.Linq.Enumerable.All[TSource](IEnumerable`1 source, Func`2 predicate)
at AjaxControlToolkit.ToolkitScriptManagerCombiner.GetScriptReferences(HttpContextBase context, String[] bundles)
at AjaxControlToolkit.ToolkitScriptManager.OnLoad(EventArgs e)
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)


It happens at random times at random pages on the site with or without any ajax controls (other than the toolkitscriptmanager on the master page).