Apple Mini DVI to Video Adapter is not working. Please Help...
Your probably not doing anything wrong. There are thousands of users with Similar issues and it seems to be with many different adapters.
We have Mini DP to VGA (3 different brands) and they all fail most of the time. This seems more prevalent with LCD Projectors. I've tested some (50+) with VGA Monitor (HP) and they all worked, LCD Projector (Epson, Hitachi, and Sanyo) and they all fail, DLP Projector (Sanyo) and one worked.
My Apple Mini DP to DVi works most of the time. My Mini DP to HDMI (Generic non Apple) works every time.
The general consensus is that Apple broke something in the OS around 10.6.4 or 10.6.5 and its not yet fixed. As we are a school we have logged a case with the EDU Support group so will see what happens.