I had no problems playing a Blu-ray disc with external decoding (HDMI bitstreaming), either in normal 2 foot mode, or (later, after setting PDVD to bitstream) when launched by Windows Media Center (which always causes PowerDVD to run in Cinema Mode).
My test system: Win 7 Ultimate 64, Intel Core i3-550 CPU, ECS H55H-I Mini ITX Motherboard, NVIDIA GTS-430 graphics with latest drivers... connected through an Onkyo TX-SR508 AVR to a Panasonic TCP50VT20 TV.
Test disc: Wall-E
Anyhow, I'll follow up with our engineers to see if we can figure out how to reproduce the problem on one of our test systems. If you have the issue, please send me a private message with your detailed system configuration and the steps to reproduce the problem. Please include a list of any other audio or video software that you are using that might possibly affect PowerDVD (Reclock, etc.), and confirm whether you are trying to play BD discs directly, or otherwise.