Purple spots hen converting avi to mpg2

[DarthJango]

Everytime I use TMPGEnc to convert avi files to MPG2 the picture will get purple areas on it during the movie. The color will be nornal then the purple spots show up for a few seconds and then its back to normal for a minute or 2 then the purple spots show up again. It does this through every movie I have converted so far. What causes this and is there anything I can do to get rid of it?

[setarip]

"What causes this?"

This sometimes happens under TMPGEnc when you attempt to increase the resolution of the file you're converting (e.g. from 320x240 to 480x480)...