Anyone managed to carry out a successful upgrade from version 2.0 of the tool to version 3.0?

I have version 2.0 working perfectly in our parent domain, and using alternate credentials can successfully license and report on the status of devices from the child domains. However upon upgrading to version 3.0 of the tool, when using the alternate credentials the progress counter immeadiately ends with a failure with no error.

Upon searching the event log for VAMT I notice event ID 1000 "Error while updating products: System.UnauthorizedAccessException: Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED)"

I'm using the same accounts for alternate credentials that were used in version 2.0.....what am I missing?