Charlie If you actually want a more helpful answer than the one given above, your going to need to provide some sort of information to us regarding your system and set up, NapMx is just an app that contacts a web site to download a list so its not likley to be a big problem your having.
What operating system and service pack level are you using and are you using the version of NapMx from our archives, also what firewall are you using a seperate one or windows only, lets hear some info from you please