Try removing the db file from the nem folder and then start NIS again. It sounds like it got corrupted somehow.
It seems to be working now, blocks are updating.
Was to early with my happiness! I have 0 NEM in my wallet
Imported your private key ?
Using the right account ?
Headover to
http://forum.ournem.com. This problem has been solved many times there.
Oh, it's ok now. Of course it had to sync starting from 0. Wallet is up to date. Many thanks for your help mate!