Bad password from net use from Win 7 to Win 8

I have 3 64-bit computers in the same workgroup on a LAN, as follows:

computer A: Win 7
computer B: Win 8.1
computer C: Win 8.1

All are logged in to the same username, with the same password on all machines, and without specifying a user / password to the net use command:

Computer A can net use a shared drive on computer B, but not on computer C, where it gets asked for a user name and password, but supplying it fails.

Computer B can net use a shared drive on computer C and on computer A.

Computer C can net use a shared drive on computer A and on computer B, although it asks for a user name and password for computer B, and supplying it succeeds.


When I turn off password sharing requirement on computer C, then computer A can link to it.

Since computer B can net use without specifying a username or password to both A & C, it would seem to verify that the passwords are identical on all machines, and when asked for passwords I supply that same password, and it works in one case, and fails with error 86 from A to C, but works fine from C to B.

I have no clue what the next step would be to diagnose this. I would like to achieve the link from A to C.