Unable to login to one computer from another -> Intermittent

I don't understand why I'm having this problem.

I have two computers in the house. Neither are in a Domain. Both are in a workgroup called Workgroup.

There are a couple different scenarios for the problem:

First, if I click on the other computer name from explorer, under the Network icon, it pops up a dialog box that says: Windows cannot access \\<the computer name>. In the description it says to contactd the administrator to request access.

If I click Map Network Drive, and Browse to the computer I get the same error. It doesn't even show the shares and let me try to enter a user name and password.

If I click Map Network Drive, and enter \\<computer name>\<share name, it pops up asking for a user name and password. I enter the user name and password, then it pops up with a dialog box again, with the user name filled in of <computer I'm logging in from>\<User name>, and just keeps popping that dialog box up again.

Now, other times, I can click on a drive that says it is disconnected (from a previous mapping that was successful), and it will pop up the user name and password box, I enter it, it fails, but then, all the folders will pop up and I have access. OH, by the way, at this point the dialog box will list Doman: < computer name I'm on>. Never does it reference anything about a workgroup.

This is Windows 7, Pro.

Screwy.
'
Any thoughts?

No thoughts, anyone?