Vista - access to shares in a workgroup

This is a question on Vista Business.

There is a workgroup with 4 workstations (1, 2, 3, 4) and 4 is sharing
a folder. 1 & 2 can access that drive by simply mapping to the share,
no name/password is required. When you try to get 3 to map, you are
asked to provide credentials.

Since the other computers can access the share properly, I would think
the problem is on 3. There is a limit of 10 users on the share, and
since 2 are connecting, I'm (I hate to use this word) assuming the
permissions for the share are correct.

I looked at the local security settings on all the workstations, they
all seem to be set the same.

Ideas? Pointers to where I'm screwing up?

Thanks!
Mike