I tried using a CTF theme, and when I did, I was unable to run any isos. It wouldn't let me change back to normal, so I tried changing ISO drivers, and when that didn't work, I connected my PSP to my PC and changed the game.txt, pops.txt, etc to have cxmb 0. I turned it back on and ran CFW again, and it allowed me to run the ISO I wanted. But all my saves were corrupted and I was unable to make a new save.

How can I fix this?

Backup the content of your MS on your PC then format the MS (System settings> Format Memory Stick). After formatting your MS copy only the /PSP/SAVEDATA/ folder back yo your MS. cxmb plugin is meant to be put in vsh.txt ONLY.