Bottom line: Intel Core i7 users might need to disable hyperthreading.
I built a HD video editing machine recently using a Core i7 920 running Windows. I fired it up, installed Windows and Movie Studio Platinum 9 (9.0b), and everything was great. My AVCHD video from my Sony HDSR12 looked great and VMS9 worked like a charm.
Then one day things turned sour. The Sony AVC encoder stopped rendering anything. All rendering would stop after a few seconds and/or crash. It was the only program that crashed. I tried EVERYTHING to fix it. I tried all versions of Windows (XP 32 and 64 bit, Vista 32 and 64 bit, 7 32 and 64 bit). When I tried rendering in a virtual machine with VMware, IT WORKED! No matter the Windows version, in a VM it would render just fine.
I was trying to think what would cause this when I remembered that between the working time and crappy time, I had enabled hyperthreading on the CPU. The fact that VMs worked and bare metal installs did not seemed to fit this since VMs do not know about hyperthreading--they get allocated to real (to them) CPUs, and the hypervisor figures out the rest.
I turned off hyperthreading and rendering worked in all versions of Windows. Hyperthreading on my motherboard was disabled by default in the BIOS, so maybe others do not hit this for that reason, but this causes me DAYS AND DAYS of grief. I hope this saves someone else as well.