I have not faced this problem. I would do the following. Search for all NEM-related files on your machine and delete them. Afterwards, install NEM again from scratch. Then it should usually work. Which WinOS do you use?
I even had the same problem after a complete new installation of my system!
At the moment I have no NEM in my Bag anymore, I sold them at 900, unfortunately
ETC is the better investment at the moment, but I will come back for sure!!