Ok, check the permission on the file you uploaded via FTP. If the permission and owner is correct, then you may need to re-upload the default style, but before doing that, I would submit a support ticket at Vbulletin.com. They will probably tell you to re-upload all non image files and see it that fixes the problem, but I would rather them tell you to do that. I hope it is a permissions issue and now feel pretty sure it is. I can visit your site and call up an image like this:
http://www.mjworldcry.com/board/images/misc/tag.png
So, things seem to be in place. I am hoping it is a permission or owner issue on the new file. My folder is set to 0755.
Maybe that is the issue.
Also, when you check the owner of the folder, make sure it is the same as the web user. In many cases it is the 'nobody' account. So, if it was being owned by the 'root' account, then the the folder information could not be seen by anyone. it must be owned by the web user account. (I hope that is clear.)