I always work with some windows shares which are password protected. It always worked when I clicked in the Finder on the share and then "Connect As...". After a couple of seconds waiting, the password dialog poped up I entered the account credentials and the connection was complete.

But know it doesn't work anymore. I don't know, what should have been changed... It also doesn't work on command line:

smbclient // --user=admin --workgroup=MyNetwork
Password: *******
Domain=[MyNetwork] OS=[Windows Server 2003 3790 Service Pack 2] Server=[Windows Server 2003 5.2]
tree connect failed: NT_STATUS_BAD_NETWORK_NAME
What is the problem? Other people still can connect to the shares...