I'm experiencing the same issue that everyone else is experiencing.  Upgraded from NAV 2007 to NAV 2009 in the last 2 days, but ever since then none of my workstations is able to connect to the computer we use as a file/application server.  All of the 9 computers (8 clients, 1 "server") have the following specs:

NAV 2009 16.1.0.33 on all computers (upgraded from NAV 2007)

AutoProtect enabled (what is the point of NAV if you have to disable this?)

All Intrusion Prevention Settings are enabled (but computers never show up on blocked list, so I don't think this is the problem)

All computers are "found" and visible on NAV's Home Network (LAN)

Windows XP Pro SP2 on all computers (all latest patches installed)

Windows Firewall enabled

Certain folders are shared on the network 

No trouble with NAV 2007

Do you think adding each computer again to "NAV's Home Network (Trust Control)" will solve this problem?  (I'm skeptical since all the computers are found in NAV's Home Network (LAN) to begin with.)

Does NAV 2009 have a "white list" where we can add IP/MAC addresses of computers we DON'T want NAV 2009 to block?  (I remember seeing a setting somewhere asking if you wanted to allow Network LAN computers to be excluded from blocking, but I forgot where I saw that...)

Every 1-2 hours we need to reset the "server" because it starts to block traffic from all the computers in our network.  Obviously this is NOT an acceptable "solution", so Symantec better solve this problem soon... because I'm getting really annoyed with this problem and tired of restarting the "server" so many times a day!