Yeah it's definitely not about the dual cards setup. I've just unplugged one... and got the same thing with single card: "The application has failed to start because the application configuration is incorrect. Reinstalling the application may fix this problem." Message is showing almost instantly after double-clicking guiminer.exe.
I've just checked this single 5770 in Caps viewer... everything seems to be OK: OpenGL4.1, OpenCL 1.1, Catalyst 11.6 with SDK 4.2 installed. I also deleted previously unpacked GUI miner folders, re-downloaded and then tried both the latest version of GUI miner (...614) and previous one (...609). Catalyst control centre also looks fine, no problems reported or hinted... yet GUI miner still refuses to launch for no reason I am aware of.
On a side note, where exactly is that poclbm.ini file (mentioned in previous post by frizzl) located? Didn't find it in Documents and setting. I've tried searching both hard drive partitions but again couldn't locate it.
I am really confused and running out of ideas. Program works very nice with two other rigs with same OS, and, tbh, lunching GUI miner is pretty straightforward procedure where average newbie like me cannot really make a mistake... or at least it looked that way until now.