Windows2000 Server License Manager

I am running windows2000 Server with Exchange2000. I have License Manager turned on. I have never had over 10 computers attached (nine desktops and 1 occasional laptop). This week for the first time some users are denied access with an error saying ?No License was available for user ____ using SMBServer 5.0?. There is nothing different from the past six months when the same users and computers have logged on without problems. When I inspect License Manager it correctly lists the users in Clients Per Seat and Server Browser but in Product View it adds them incorrectly showing more Per Seat Reached than Per Seat Purchased. Rebooting does not solve the problem.