In 8.04, 9.04, 10.04 and 11.04 I have been able to connect to a Windows 2003 server. It has been simple and effective.
Since loading 12.04, I can't do it. The error highlights the password (which works on the 11.04 laptop beside it). In fact, no password is acceptable.
I have tried it with Ubuntu and Xubuntu 12.04 with the same result.
Likewise, the answers posted with "Cannot connect to Samba share from Nautilus" have not resolved the issue.