I installed the post service pack 6(a) security rollup on my NT 4.0 box. I am running backoffice 4.5 with Exchange 5.5. Immediately after installing the security rollup, which includes ALL hotfixes etc.. since sp6(a), email clients could not log into the mail server to check their mail. They get an error message stating that there aren't enough client access licenses. This never happened before. There aren't that many clients anyway. When I look at how many users are currently logged on it shows the Administrator logged on 9 times. I uninstalled the security rollup and it works fine now. However, there are a lot of security fixes I would like to have on my system, but I would like the few users I have to be able to check their email. And, I read a Knowledge Base article that said you don't need a CAL for a user who is only accessing the Exchange Server anyway (and is not using file shares or print shares etc...). Does anyone have any idea what happened and how I can correct it. Thanks.