random lockout on 98 clients

We have a new 2000 network up and running. It consists of 1 PDC and 4BDC's and 1 member server. And our problem is that our 98 clients keep getting locked out. It's not consistent with any one user. We have a 2000 SQL database running that the users access. When the lockout occurs it is usually in the middle of a session. A message pops up after a long period of time saying connection failed. After they reboot to establish connection thats when they get the messge saying they cannot log on to the network, then we have to go and unlock their account.We have checked the lockout policy, it is correct. We have checked everything that we could think of. If you help us it would be greatly appreciated.