does the /admin directory exist? Did you double check the config-int.php not the config-inc.php files to make sure ALL the directory paths are set? I've overlooked a path in the config-int.php more than once myself. I registered in your forum and wen to the gallery and it looks fine from the user side. But I definitely got a 404 when I tried your admin page.
Well, the strange thing is that the 404 messages references the wrong address...my forums directory is forums, not forum. But, it is properly entered in the config-int.php file. Is there somewhere else it could be incorrectly stored?
Then it has to be a path typo somewhere. Double check the paths in both the config-inc.php and the config-int.php and you may want to manually browse the settings table for photopost in your MySQL database. I've had to manually correct it after some upgrades before.
I did change some stuff there...thanks, memdy. I'm really good at following directions, but I really don't understand what all this stuff means and I'd never have thought to do that. It seems to be working, now...knock on wood !