Incorrect subnet mask

We recently moved from one lan system to another. On the previous lan we used subnet mask 255.0.0.0 and on the current system we use 255.255.0.0. The current system is using win 2k server. Ever since the cutover we have had a problem with some of our win98 PC that for some reason get the old subnet mask (255.0.0.0) in the IP Config and subsequently they can’t log in until we do a winipcfg and the subnet mask is correctly change to 255.255.0.0