You must be trying to run UI2 with alpha blending. To run UI2 with alpha blending you need the following:
1. Nvidia 6xxx or 7xxx series card. ATI cards apparently don't support this.
2. You need to have the "nvidia" driver installed (NOT nv in your xorg.conf file)
If you can't get this working then drop back to using plain old UI2. You can launch the AV wizard again by rebooting the box and holding down shift.