This is a definite 100% bug under Mac OSX 10.4.10 and probably other versions.
Keepassx will no longer accept your database, say the file is corrupt, it will even stop displaying the the .kdb files as supported databases when you try to browse for your database.
FIX (Sad that Mac users need a windows Fix): Install
Keepass on a windows computer, load your .kdb file from your Mac that is said to be corrupt. This should work, the Mac KeepassX incorrectly reports files as corrupt when in fact they are just fine. Go to File > Export > Keepass Database. This will ask you to keep or change the key, you can just go ahead and keep it. Then save the new database as a new file name, copy it to your Mac and then KeePassX will recognize it.
I had to completely re-install my OS to figure this out. With a fresh install of 10.4.10 and the only application running KeepassX, I knew the software was broken. The developer of the software simply said his is a corrupt file and that was the end of it. I told him a CD file does not change and would not be corrupt. He refuses to accept a bug in his software. Sure its GNU, but I mean, this is keeping peoples passwords, its not some simple app for nothing. Either support your software, charge people some $ or give up the project. Don't release buggy code which could cost people time, $ and especially their security.