After installing the 1.03 update I could not start ARMA2. At startup I would see the row of ticks followed by a brief black screen then a CTD with an error message window stating "Error compiling pixel shader PSSSSM Specular Alpha:1". After some searching the internet I could not find the same error message but reading about other "Error compiling pixel shader" errors I ended up reinstalling version 1.01 from dvd and patching that directly to 1.03 which seems to work. I was some way through Badlands before the 1.03 update and cannot resume the mission but a revert seems to be working so far.
Thought I'd post this if any others are having the same error.
System specs at the time were:
Win XP SP3 32bit
NVIDIA GeForce Driver Release 190.38 (and tried 186.18 WHQL)
Intel i7 920 CPU
Gigabyte EX58 Extreme MB
2 x Gigabyte GTX 260OC's in SLI
6Gb DDR3 Corsair XMS3 triple
Swiftech H20-220 Apex Ultima Water Cooling System