Ok, I posted this question 8-10 months ago (I think), and I never got an answer. I can no longer find the original posting to check if anybody offered any solutions (was it deleted?). I was able to find my post mirrored on some other site, so I am reposting it here now in hopes of possibly getting an answer... I recently upgraged my machine from a C2D 6750 to a C2Q 9550. I also took this opportunity to do a fresh install of Vista Ultimate x86. I am using EE2 to encode vc1 video and Media Encoder 9 to encode 5.1 audio. Now whenever I use the Stream Editor tool that comes with Media Encoder 9 to mux the two together, I get corruption. No two muxes are the same size, and will randomly get video skips/speedups and/or audio blanking. If I reinstall the C2D processor and do another fresh install, the resulting file comes out fine, and the file size is the exact same over multiple muxes. I currently have Stream Editor working on the quad core through a virtual machine, but would like to be able to just use it like normal. Does anyone have any insight on how I can resolve this problem? or am I stuck with my vm method?