Tags not displaying: DBCVT can't convert file?

Basically, iFix will open and all the tags will display if I run it in DEMO mode. Closing and switching to runtime mode leaves me with all the tags displaying asterisks: ***

When I open iFix in runtime mode, I get an error:
"ERROR-9016: Errors occurred during database conversion. For more information refer to the error file"

I look in the error file and it gives me some not particularly helpful information:
"ERROR-9009: Database version is not supported by this conversion program"

I have backups of the PDB folder, if I restore it, I can open iFix in runtime mode. If I ever open it in the demo mode again, it gets corrupted.

I've tried running DBCVT.exe while iFix was running, it just flashes and then closes.

If I open iFix with the "corrupted" PDB file(s) in DEMO mode, it will start up with no errors and display all my tags perfectly.

This project was previously on iFix 5.0, but I had no trouble upgrading to 5.5 on a machine with identical hardware and the same exact project files/configuration.

I'm at a complete loss here, ANY suggestions would be a huge help!

I'm running:
Windows XP 32-bit
iFix 5.5
Historian 4.5

Edit 1:
I tried repair iFix, and that was a complete failure. It wouldn't register a couple of DLL files upon restarting. So, I uninstalled iFix and related components before reinstalling. The reinstall was successful, but I'm still having the problem described above.

I also tried disabling DBCVT.exe in the FIX.ini file. I no longer get the error 9016 popup when I start iFix, but I still get asterisks. I re-enabled it.

Edit 2:
I just copied the working project from the sister system and it gets the same error when I try to open it on this problematic, second machine.