Install a 32-bit version of AviSynth and do the "IVTC" outside of StaxRip. Or let those few frames of chroma nastiness remain after being IVTC'd within StaxRip. It's not as if you or anyone else will notice it when played at full speed. Or ask the developer to make it possible for you to use SRestore within his program. He can be found in the
MPEG-4 Encoder GUIs Forum here on Doom9