Working now. I had an old x64 TIVTC.dll from 2010, don't know why :-/
No problems with:
https://github.com/pinterf/TIVTC/releases
EDIT: I guess I took it from this (outdated) list
http://avisynth.nl/index.php/AviSynth%2B_x64_plugins
EDIT2: But it's still interessting that it only crashes in VS and not in VdubMod