John,

 

Now I guess that is an proxy/firewall issue.

 

Because for the silverlight XAP file, our server code do not provide header 'Content-Type' for it,

 

And the firewall may not allow the XAP to be downloaded , so the button keep disabled and waiting silverlight load.

 

We have add 'Content-Type' for it. Please try again.

 

Regards,
Terry