4
Did you run checkit.php on a execution time set to 90 (or maybe more)? did you get the timeout error?
What kind of computer have you running? I have 900 MHz Athlon running, and the checkit.php needs some seconds (7 or more seconds I think) to run.
If PHP Debug is really on, we should see an error message instead of a blank page.
A blank page could be caused by wrong files, corrupted files, missing files, corrupted database, wrong file/directory permissions, incorrect setting in mainfile.php, old PHP version (I'm not sure), wrong settings in php.ini (I'm not sure) etc.
If there is something wrong with my enumeration.... let me know.