https://server:8443/core/config pag check the credential test.
I am afraid that you are putting in windows user name and password in the field of domain user name and password ?
The core config page test works fine with the username and domain in two separate boxes.
The setting up of the mvm server within ePO is the issue..
I am using the same username and domain, just in the form xxx\username in the mom setup page.
I am using the same host name on both pages..
I stress..all this was working previously...it is the nature of the error that concerns me as both the mvm/SQL/ePO servers are all in the same domain..