Prob w / Win 95/98 PCs after Server upgr

After upgrading our servers from NT 4.0 to 2000, our Win 95/98 clients are getting this error message when they turn on their PC in the morning: “Error connecting to the network, try again later”. The PCs that have 2000 Professional are fine. This doesn’t happen every day. Has anyone seen this one? I can’t find anything in Technet on it. Thanks in advance.