[HELP] can't encode but displays finished

[Selur]

vapoursynth.Error: Filter LWLibavSource returned zero or negative frame count

-> LWLibavSource can't handle your source clip.
Since it works fine here, it highly likely there is something wrong with the clip.

Also try:
a. (if you have an NVIDIA graphic card) enabling "Filtering->Vapoursynth->Source->Use DGDecNV when available" and see whether the preview works
b. disabling "Filtering->Vapoursynth->Source->PRefer LWLibAVSource over FFMpegSource2
If both do not work then the cause probably is your source video.

Cu Selur