Need help converting Monster Hunter Freedom 1 save to another region

[LunaMoo]

Coldbird's server allows playing different regions of MH games together since they ARE compatible. If your savedata isn't compatible after simply renaming(at least assuming it's EU<->US versions which should work fine with each other) then most likely you were playing a game modified to run on outdated psp firmware.

No idea how such patches worked as they were mostly used by pirates and have no idea if the savedata made by game modified in such way can be fixed. But I'm quite sure this could also be the real cause of your adhoc incompatibilities and if I recall others having problem with it - that "mod" will also stop you from being able to transfer your character to newer MH games.