sony vegas error? :/

ive been having this for a while now and asked a few ppl if they knew how to solve it and tried a few things myself but i always thought i might aswell not use this in movies but now it gets pretty annoying.

its as following: when i want 2 clips running at the same time in like split screen i get these weird stripes ( blue white green and shit) also when i use some transitions i get this. ill show a screenshot here

http://img165.imageshack.us/my.php?image=weirdstuffbt6.jpg

thx in advance