Unexpected Error when renaming/ fixing roms

[Former user]

I get an unexpected error. Operations will stop. The process cannot access the file because it is being used by another process.

Then the renaming will stop but 1 or more of my rom files will end up with a weird ending format and will be unusable.

I'm trying to rename 3DS files that need their rom names fixed.

I've restarted my computer, shut down all other processes, tried to search online for all fixes but it just wouldn't work after retrying many times.