Difficulty mapping remote network drive

The difficutly I am having is this;
I have a clients system that at one time we could dial up and map the drive. Now the IT department has built a new server. I can dial up and access the system via VNC and can run the programs on the remote system. I have checked the rights and have privlidges to access the drive. Yet when I try and map the drive I get “Unknown user ir password”
Any suggetions would be very much appreciated.