Vista - Backup Vista to XP (repost with additional info)

I am still looking for a solution, to why I cannot backup to a an XP machine
from a Vista machine.
I am running XP home and Vista home premium.
The network is humming along just fine, all shares can be accessed and
written to, whether XP to XP, Vista to XP or XP to Vista, no passwords or
ID's are required.

Backing up between XP to XP had no problems, backing up XP to Vista, no
problems.

Now backing up Vista to XP, is a no go. It asks for and ID and Password. I
have tried all that are setup but get the same error message.

The network share could not be accessed for the following reason:

No mapping between account names and security IDs was done.
(0x80070534)

Please ensure that the network location is valid.

The location is valid, as I have mentioned, I can read and write to the
share no problem. The IDs are valid I am using them on all machines.

Is there a solution?