Problem with .avs file

[dbhta]

Hallo.
I'm having some problems and i was wondering if someone could help me.
I've ripped a movie (4:3, NTSC format), made the .d2v project,
made the .avs script from GKnot, frameserved it to Virtual Dub,
and finally encoded with Divx 4.12 (2 pass).
The problem is that at the middle of the movie i get blocky picture
and the movie seems to jump back and forth.

I view the movie fine in DVD2AVI, so it's not a problem of DVD2AVI.
It has to be a problem of AviSynth or mpeg2dec,
cause when i open the .avs file from Virtual Dub and view the input video
then i see the blocky pictures and the choppy playback.
The thing is that i see the movie correctly in PowerDVDPlayer, so the vobs are not corrupted.
Any ideas?
Thanks in advance.

[ookzDVD]

@dbhta,

I think it's interlaced material, so make sure you use the proper
filter to handle it.

[Didée]

Could it be that you are using the *.d2v-file that was generated by Smartripper? It creates some, but this one behaves very ... strange.
Be always sure to use the *.d2v created by DVD2AVI.
Just a spontaneous idea, could also be something completely different.