new to 3ds model extracting

hi, im rather new to ripping models from 3ds games and am having an issue with getting the models from my decrypted rom, everything goes fine until i try to extract something. using command prompt and the ctrtool i get : Error, IVFC segment corrupted and Error, RomFS corrupted. both the un encrypted and encrypted files are the same size (according to the tutorial i read they have to be)

any info would be appreciated, thanks in advance.