Map a Drive to a Vista Client from a NT 4.0 Server

I?m trying to map a drive from a Vista Client to an NT Server 4.0.; when I enter the user name and password to connect I get a message telling me that the password is not recognizable which I can’t figure out why, because I use the same exact User name and Password to connect my mapped drive from my Windows XP and it works fine. Could Anyone Please explain why my NT Server doesn’t recognize my User name and Password when I use my Vista client to connect to the NT server. Thanks big in advance!