UBB.threads PHP Forum Software Community Forums UBB.classic [Archived] UBB.classic Bugs preview message not working in 6.7.3

I've recently upgraded my board to 6.7.3 and whenever I reply to a message in the forum, if I click on ‘preview message’ the small window that appears actually take you back to the forum main page and not a preview of the message.

Any idea how I can fix this?
Here's a link to our board-
Foot Talk Forums

Thanks,
Steve

Do you have any modifications installed on your forum?

I'm leaning towards the frames + redirects as the cause of the problem.

I'm going to move this to Post Installation Troubleshooting since using frames is a bad idea. If you can duplicate the issue without frames, I'll move this back to bugs.