Avid codecs

have a very strange problem that is happening to me, and maybe this is not the correct place to put this question. Anyhow. When I render or convert anything to any avid codec when it is compressed, it comes out corrupted. The frames have this chunky broken jpeg damage looking thing to it. HOWEVER. If I first render something uncompressed or at animation codec, then convert it to DNx36 it comes out fine. So basically If I export something out of the avid at DNx36 same as source (or any kind of avid codec) and then do vfx work on it in shake or something in final cut, then render it back to DNx36 its corrupted. I have to do an intermediate step where I have to render it uncompressed then do another conversion back to DNx36 and it works fine?!!

This problem spans across every single program I try it in. Quicktime, avid, shake, final cut, etc. I've tried re-installing the avid codecs, re-installing quicktime, etc. I've also tried this with Tiger and Snow leopard, and different versions numbers of al the programs. Not sure what is happening? This never happened before and is crippling my work flow.

Anyone have the same problem, know a solution, or have any other suggestions?