Bought the game today. I have an original CD version, and played through most of the campaign years ago. The gog version works, I could play the first two missions, but on the third mission "Sven Carlsson" it's stuck in the Prepare for Battle screen. Anyone got tips for fan forums on the game (who maybe offer fixes)?

Be happy that you got that far, many people had that error at the first battle.

I hope gog don't leave it that way. I hear the music, but the mission never starts. BTW, I'm on Windows 7 64 Bit SP1.

Same problem here - also on Win7 64bit: The previous missions worked, but the Carlsson-mission stucks in the loading screen, while music continues in the background.

I've filed a support request. Hope they'll reply. I'd like to continue my playthrough.

Please try the following, worked for me. I got the solution from support:
To make sure that no third-party applications are interfering with the game, please try to install and run the game in "clean boot" mode. Instructions on how to do that can be found here:
http://support.microsoft.com/kb/929135

Please check the language setting for non-unicode programs and if it is not set to English change it and reinstall the game:
http://windows.microsoft.com/en-us/windows/change-system-locale

I think it was the system locale that fixed it, because it now also runs with the disabled services (clean boot) re-enabled.
Changing the music output in main menu could also be worth trying (from General Midi to FM soundcard).

This is the same response I got and it worked for me as well. Then I went through trying to figure out what was causing it, and for me it is Adobe Creative Cloud. If I have that running then the game will hang at prepare for battle. When I close the program entirely then the game loads just fine. I hope this information helps someone.