new to 3ds model extracting

[Flareon136]

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.