Windows 7 - Another 7/XP Network Access Problem (only different)

There are many Windows7 <---> XP network/sharing threads here , but I didnt see one like this:

3 Computers.

a. Windows7
b. XP
c. XP

a and b have the same account and password, c's is different. All 3 are in WORKGROUP. The time is correct on all 3.

a has network access to c
b has network access to a and c
c has network access to a and b

a cannot access b.

Using the only account on a, which is the same as the account on b, I get the Enter Network Password window showing Domain:computer a. It fails and asks again for computer a/username

I've checked the local security policies on b and c side by side. These are the only differences:

c
Accounts: Administratior account status = Not Applicable
Accounts: Guest account status = Not Applicable
Network access: Allow anonymous SID/Name translation = Not Applicable

b
Accounts: Administratior account status = Enable
Accounts: Guest account status = Disable
Network access: Allow anonymous SID/Name translation = Disable


The same thing happened with Vista on computer a and it resolved with no action from me.