Simple questions but need to be asked:
1) what are you trying to render to? GPU accelerated encoding is only for mp4/h.264 encoded files. Either the Main Concept or Sony codecs.
2) In the options menu under video, how much memory do you have set for the Dynamic Ram preview? If you have anything higher than 256MB, try reducing it to 128MB and see what happens.
3) Also for rendering options you should see a drop down on whether to use CPU, or GPU. What do you have set? You need to set this to GPU.
4) Lastly (I forgot where this is, but I think it's under Options and then the Video Tab), you need to make sure your cards are selected from the dropdown menu. If the cards aren't listed, then Vegas isn't recognizing them. This could be because they don't have the latest or supported driver version.
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http://www.davelozinski.com
http://www.davelozinski.com/DemoReel/
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