access smb share via emacs tramp mode - repeatedly prompting for password

If I use smbclient from the command line on a unix host to access a windows server share (happens to be a windows server in an Active Directory domain), it works fine. I can access directories and files on the server. Here's the smbclient command that succeeds:

smbclient -U user -W domain -I ip_host //sharetop

So now I am trying to use tramp mode in emacs to open (find-file) the following url:

/smb:user%domain@ip_host:/sharetop

I get a password prompt as expected:

Password for /smb:user%domain@ip_host: 

However, when I enter the correct password (same one that works with smbclient), it just shows me the password prompt again. And the *Messages* buffer has:

Tramp: Opening connection for //user@ip_host/sharetop...failed

I'm looking for success stories with emacs tramp mode accessing files on smb urls that point to windows servers. Or perhaps a way to get more information than just "failed".

Update
I set tramp-verbose (Traces) to 6, and that showed the smbclient command line:

smbclient -g -L ip_host -U user -W domain -s /dev/null

-L is intended for the netbios name. In my case, I am using an IP address or DNS name. So, it appears I'll have to figure out how to convince tramp/smb to accept an IP address instead of a netbios name.