Windows login rejected by linux server

I have a client that is using a RedHat 7.0 server, running samba. I have four PC’s that are able to login to the server, but when I added a laptop to the domain I get an error saying that either my password has been typed incorrectly or the server is rejecting the login attempt. I am 110% sure that the password and username are correct. Does anyone have an idea about what could possibly be wrong with this thing?