Hi.
It does not copy over a folder as such that says Oblivion. It copies over Oblivion.exe plus .bsa files meshes/textures/sounds and misc.
Are you running normal Oblivion or steam?
If its normal Oblivion. You should not have to disable your UAC.
Uninstall Nehrim completely. Reinstall to i.e c:\Nehrim. If oblivion.exe and bsa files do not copy over this time. Question - how much disk space do you have? Sounds silly but I have seen someone try to install when only a couple of gb left. When installed, start launcher, ensure only Nehrim data files ticked - there are 3 of them. Will crash if oblivion.esm ticked.