NT Outlook/Exchange Error

Winnt 4.0 Srv,Newer HP Srv/Outlook 2000/MS Exch 5.5:This morning after creating a two new user accounts as we normally do,they received the following error: “Unable to create Outlook folder on server,check user permissions” Deleted account,recreated.Same problem.
–Never had this problem before.ANy ideas?
Also,names/alias are spelled correctly;access permissions are set correctly on the server and on their individual home folders;folder is mapped correctly.