Hannibal_Barkar: The problem is that the DVD version has a slightly different .exe file than the CD version, modified so that the game looks for a DVD rather than a CD. Because you "de-patched" to 1.2, the game doesn't realise it's supposed to look for a DVD in your drive rather than a CD. It can't find it, so it spits out an error.

I'm afraid there's not much to do except wait for 0.8.