Missing ground in snow valley

[jens]

Did you make any changes to the settings between playing the first time(when you had no errors) and the second time when the errors re-appeared?

If so go to My Documents/Penumbra Overture/ and delete the settings.cfg file, then start the game again to use default settings and see if that works. You could also try to turn the settings down to minimum and see if that helps, and then step by step turn them up to pinpoint more exactly what could be the problem.