Ok, Iv' seen someone else with a similar error message, though he couldn't get the game to run at all.
What worked for him was re-installing .net, and then re-installing Obsidian. Il' point out that he said he'd allready tried re-installing obs, did not work. The game did not work properly after merely reinstalling .net either - it had to be re-installed after that.
Although it doesn't say much, here's the thread:
http://www.dxgaming.com/phpbb/viewtopic.php?t=10407
Hope this helps.