Forum Attachments and Thumbnails
 

I have just upgraded from 3.8 to 4.04. The upgrade worked with no Errors. I'm having an issue where thumbnails will not generate. I can add new attachments and view them. I can view existing attachments just not as an thumbnail. I have check the attachment manager and everything is enabled. I have check the global settings and thumbnail is set. What am I missing or is this a bug?

Thanks