Remote Desktop Log In

Its my first time using Microsoft Remote Desktop and for some reason, I cant log in to my user account. Its giving me an error ...

"INVALID USERNAME OR PASSWORD".

How can that be since I use that "administrator" account and password all the time? It appears that i'm connected since I could see the login screen and my account name, it also displays the "Windows Vista Business" (the OS for the PC that i'm trying to connect to) at the bottom part of the screen.

I did the port forwarding 3389 TCP/UDP definitions, allowed RDC on norton firewall settings.... am i missing something ???

I'm Desperate!!!... HELP!