There's a bit of info at the Windows Mobile Blog
Happily titled "Who is GWES and why does it keep apologizing?"
http://blogs.msdn.com/windowsmobile/...ologizing.aspx
Basically if any poorly written program does something stupid with a window, GWES complains and gives this error. You can disable the reporting and you'll never know there was a problem but in that blog he says they actually *like* getting those reports so who am I to take away their fun?