SPFW slow/killing file copying across windows network - please help

I have Sunbelt PFW installed on 4 PCs (along with VIPRE) on an internal gigabit switched network and am seeing *very* slow file transfer and file transfers that suddenly drop without warning due to SPFW on the receiving PC treating the file transfer as an attack.

More info:

The PCs are 2 x WinXP SP3, 2 x WinVista32, and they all have the correct "trusted" network properties set up in SPFW.

Copying small files across the network is slow - Windows Explorer in Vista on the host PC reports file copy across the network at 5 mb/sec when SPFW is running, but this jumps to 13 MB/sec when SPFW it is disabled on the recipient PC and 20 mb/sec when disabled on the host PC as well.

Worse than this are the random dropouts - file transfers suddenly drop without warning, seemingly due to SPFW on the recipient PC believing the file transfer to be suspicious network activity.

The log on the recipient PC shows the following "[denied]" activity at the time the network connections are silently dropped:

NETBIOS SMB-DS DCERPC LSASS DsRolerUpgradeDownlevelServer exploit attempt
NETBIOS SMB DCERPC LSASS DsRolerUpgradeDownlevelServer exploit attempt

(I have VIPRE installed with latest updates on all 4 PCs, so would hope this is not actually suspicious activity, but rather SPFW thinking the file transfer is a false positive).

Please advise how to set up the SPFW and VIPRE on all 4 PCs so as to achieve the best functioning internal network - right now these PCs can't talk to each other.

Thanks for your help