Recently I was creating a Sandboxed Compatible Visual Web Part to display an AJAX Bing Maps control. When I added the Web Part to the page for first time to test it I received the following error.
Unhandled exception was thrown by the sandboxed code wrapper’s Execute method in the partial trust app domain: The UserCodeToken is invalid.
I was surprised when I saw no one had posted a solution to this issue on the Internet. To make the error go away I simply reset the SharePoint 2010 User Code Host Service.