Just setup new network, server = brand new Dell server with Server2003R2 , and 10 workstations, again all brand new running XPPro. Server is providing DHCP + DNS , and is also a file server. AD is installed. Network is behind a FW, Server has AV and clients have AV + software FW (AVG SBS edition) Everything works as it should, but sometimes (once in 3 weeks at most) when a user logs in to a workstation, after they enter there details and logon, the logon boxs appears then immediately logs off again (before desktop loads in). So the user has to enter login details again - and this time it logs in fine, always 100% OK the second time. So when the problem appears (as I say its very infrequent) after logging in for the second attempt always works. It happens with different usernames, and different workstations. Anyone ever experienced this? Setup is Router/Modem/FW - Switch - PCs Thanks