I haven't confirmed that is the cause yet, but I'm guessing it is. When you enter the thread URL, it's supposed to be
http://www.site.com/forum/showthread.php?t=1234. vBSEO changes the thread URL to
http://www.site.com/forum/forum-titl...ead-title.html. I'm guessing if you "reconstruct" the thread to the expected format (first link), and not the vBSEO format, it will work. Obviously, this is something beyond what most users will be able to figure out. I'm working on some bugs with the Paypal Donations hack. When I finish that, I'll do some testing.