cant log into live communiation

Hello,I am using live communiation in my office and have
run into a problem. Several different client PC's are
unable to log on to messenger. It says that the user
password or name is wrong, they are not. We have it set
up for over 20 people but about 10 or so more are unable
to log on from any PC. Any help at all would be welcome.
Thanks Trish

Thanks dear Trish for your support
Cheer