The MaxFileSize property is an int - this means a limit over 2GB can't be set. Please change this property to a long. 

RadAsyncUpload throws a javascript error:

SCRIPT16389: System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Windows.Browser.ManagedObjectInfo.Invoke(ManagedObject obj, InvokeType invokeType, String memberName, ScriptParam[] args)
   at System.Windows.Hosting.ManagedHost.InvokeScriptableMember(IntPtr pHandle, Int32 nMemberID, Int32 nInvokeType, Int32 nArgCount, ScriptParam[] pArgs, ScriptParam& pResult, ExceptionInfo& pExcepInfo) 

when Silverlight module is used and uploading is canceled.

The RadAsyncUpload control is used on forms with other controls, and sometimes we need to validate the control, that is require that the user uploads a file before the form can be submitted.  We have to use a Customvalidator and check the controls client-side properties to see if it has a file.  But if you set the ControltoValidate property an exception occurs.  
Please support this property so that a radAsyncUpload control can be associated with an ASP.Net validator.

Workaround:
Set DisablePlugins="true" or
set RenderMode="Lightweight"