I have the same problem since 20 days. Some suggestions;
-Using the "Delete all board cookies" link at to bottom of the forum page
-Clearing browser's cookies and history
-Trying a different browser
- Logging out and re-logging
didn't worked for me. The interesting thing is this bug didn't effect all users.
Tom Did some random users like us, were blacklisted from uploading to Arcade? Or is there a limit for total games per user?