There are two methods to properly setting up Gnapster behind a firewall. This will severely limit your ability to use Napster because all users that are configured this same way will not be able to upload to you. The most likely cause is that you have misconfigured your download directory and a slight bug in Gnapster 1.4.1a doesn't properly report the error message. Try verifying the download directory to make sure that you have write permissions to it. If this still doesn't help, then you are likely firewalled, and should see 1b .
Opennap servers distribute all searches between all the linked servers in the network.
This means that if one node of this link is lagged or not responding at all, the search will take a very long period of time. This will cause Gnapster to query only the opennap server you are connected to. The NOT search fields are an opennap extension only. Gnapster does not do the regular expression matches in the search queries, that is up to the server. This option simply passes an argument on the search that only opennap understands.