currently no logon servers available

This is a common error we have experienced within our LAN. We have a small network running Win2K Server, 2000 Pro workstations and some 98 machines. Have done clean install on server. We are using a wireless modem, Sprint Broadband for internet connectivity. We are using tcp/ip for this with static ip’s outside the network and netbeui for our LAN. “There are currently no logon servers available” message occurs far to often for this small of a network. We searched hi and lo, can someone help?