I know there was a thread about this earlier that I'll try to find, but after installing V11 latest build last weekend, I now have only one rendering template in the Sony MP4 encoder that will complete a render in Vegas 10. MC mp4 seems to be doing OK. Tried in both 32 and 64 bit versions of V10 and now can only render to the setting that currently comes up as my default Sony MP4 setting - SD, 8MB video, 256k audio. Change any parameters and I get "Vegas has encountered an unknown error" when I try to render.

I thought V11 was rendering Sony mp4 OK when I tested. May have to try adjusting all the templates and see if it really works in 11 or if I didn't dig deep enough.