I'm having the same problem. I understand that a previous user with this problem managed to fix it by running the installer again as an administrator, but I'm having no luck with that. (I also made sure to deactivate all of the other mods I'd been using, and to activate the Nehrim mod.)
Edited to add: I checked the stickied topic. I copied the files listed into a folder called "Nehrim" on the desktop, and installed Nehrim into that folder, running the installer as an administrator. Still not working. I do have antivirus running (McAfee), but I don't know if that's a problem.