That may be the problem. If I remember correctly, the original version of NWMax doesn't work with some of the newer versions of 3DSMax.
Download the version that I keep up to date NWMax Plus
Scroll to the bottom of the linked page and press the Download button.
Delete any of the original NWMax files from your 3DSMax/Scripts folder.
Unzip the downloaded file. Copy the unzipped files to your 3DSMax Install directory. Start 3DSMax. As I said earlier NWMax Plus should autostart.
MDA