When I first ran Vegas 4 I got a system error about an "invalid entry point into wmvcore.dll", but Vegas ran okay anyway. Later I ran Windows Media player (ver 8) to play a WMV file and the player complained that I didn't have an appropriate codec on my system to play ver 8 encoded video streams. The player downloaded and installed the codec on it's own and proceeded to play the video without issue. Now when I run V4 there is no error.
Maybe the installer for V4 is hosing the WMV codec on my system somehow?
Running Win XP pro, SP 1. BTW - I did download and run the MS patch to get the WMV export working in VV3 months ago.