This error occurs when your server informs the UBB that it can not create a new file for the thread.
However, the version you are using contains a few issues, including inaccurate or inprecice error messages, that may be hiding the true issue.
Please check with your host to ensure you do not have a file quota. If you do have a file quota, you will need to have it raised or prune some posts from your UBB.
After this issue has been resolved, it would be very wise to upgrade.
