I have the same issue. If I just place the control on a page the upload button starts blinking (enabled, disabled) faster and faster. Causes Firefox to stop responding after a while.

 

Running on framework 3.5. Tested on IIS6 and IIS7. 

 

Works fine in IE.

 

I can provide a URL for debugging if required. But please, get this fixed. I already purchased the license and would like to be able to deploy to prod soon.

 

Tom