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"

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.