I created a sample project for you with RadAsyncUpload control in a user control. Please download the attachment and test it at your side. Try to change the page to reproduce the issue and send it for a local test.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed