Second half of dvd to xvid conversion is a blocky picture

[deadhippo]

Im using gordion knot to convert ntsc dvd (29.970) to xvid
i have already converted about 10 similar dvds with the same software
they were fine
this dvd seems to be fine too until it is ripped

this dvd shows a blocky picture for the last half of the movie
the last time seemed to be only for the last third of the movie
and the previous dvd i also came across this problem
after several attempts i decided to use divx
it worked so i assume this problem is connected with xvid or xvid settings

i used codec sniper but found no broken codecs so i removed nothing
i unistalled xvid and reinstalled it (XviD-1.0.2-29082004)

ive used this guide to the letter - GKnot 0.32.0 ILLUSTRATED GUIDE v.8 by dap & js

at least i think i did
i think the problem here is probably very simple but i cant figure it out
and basically i need to let my pc run overnight to see if the rip was working or not so it takes a long time to check it
i know i can use divx but id prefer to use xvid

so if anyone has come across this problem
or can find a thread that you think might help me (i couldnt find one) id really appreciate it

[Hardcoreruss]

Can you rip the dvd to your drive ok?

[celtic_druid]

Only way I can think to reproduce the problem is using zones to set the jast part of the movie to say a high fixed quant. Think GKNot has a credits option. You aren't incorrectly setting it to during the movie?

[deadhippo]

Can you rip the dvd to your drive ok?

no prob from the dvd, and it plays fine in gknot

[deadhippo]

Only way I can think to reproduce the problem is using zones to set the jast part of the movie to say a high fixed quant. Think GKNot has a credits option. You aren't incorrectly setting it to during the movie?

i dont think i adjusted anything but ill have a look into that just oiin case

thanks to both of you for the reply