Should be a graphic setting problem.
1) Configure your video settings in Oblivion, and run the original game once.
2) Then go back to the Nehrim launcher, and try different video settings. (Lower textures quality, set the RAM use to 1024, decrease the anti-aliasing...). Worth a try... I can't assure you it'll work. Though most of the freezes, crashes, or video glitches I got were solved using the right video settings.