If you have Facebook turned ON for your community and some of your members claim to be getting a file download request
xd_proxy.css. You're not alone.
http://forum.developers.facebook.net...php?pid=312711
http://www.google.com/#sclient=psy&h...q=xd_proxy.css
Edit: added screen shot
Disabling Facebook Integration seems to work as a temporary fix, until Facebook resolves the issue (its what I did in my community)