Same thing happened here. I did a post in the img gallery. The first photo that shows the title but doesnt not appear is the originally 2.47mb file. The one that does appear after you click on the post is the resized 640x480 file. The only difference in the two files is that the "JPG" is lowercase on one and uppercase on the other. Heres the link.

http://www.ubbcentral.com/forums/ubbthreads.php/galleries/215791.html#Post215791

?? Any suggestions?

You might want to check the upload_max_filesize in your php.ini file if this is your server. If that's smaller than the file that is being uploaded it will fail. And the way PHP fails at that point, we can't catch it to give the user an error message (still working on that).