NT Error 5

This means that the password or user name supplied is invalid. Also, this could means that the user entered a domain name like "PACBELL.NET" in the login screen where the field should be blank.

By checking the error log you will get an invalid user entry like this:

Sep 18 17:40:48 tnt1-e1 snfc21

ohlone Invalid User pacbell.net\tuser

Have the user clear the domain name field in the Connect To dialogue box.