I got the same problem. That is the hotkey of a windows-link not set by the nv system monitor (therefore the setting in the program doesn't work)
I finally found that link in the start menu within the "NVIDIA Corporation" folder. don't delete it, it wont disable the hotkey.
Open the properties of the link, there should be a textbox calles "hotkey" with 'CTRL+ALT+M' in it. Click in the box and hit backspace, then apply/OK. now the hotkey is disabled and we are able to type the µ again. (now you are free to delete the link.. or not).
Fonte Pastamod: link
Confirmação por tentativa própria.