Just had this problem and fixed it by renaming the NMM folder. If you do this you might not be able to download via manager because the path is no longer the same so just run NMM as administrator, go to settings and disable "Associate with NXM URLs" click Ok, and enable it back again and it should refresh the path.
Nexus Mod Manager Won't "Open"
in Open Beta Feedback
Posted
Just had this problem and fixed it by renaming the NMM folder. If you do this you might not be able to download via manager because the path is no longer the same so just run NMM as administrator, go to settings and disable "Associate with NXM URLs" click Ok, and enable it back again and it should refresh the path.