Thats error is at the beginning of the add wizzard process. Did you reimage the FS850? You will not be able to add it again until its been re-imaged. It might be quicker to just log into the MWI interface and point the Foundstone Configuration Manager to the new FCServer. That will upgrade it to the correct version and reset the DB settings.
I had the same issue with an MVM 3000. All I did to fix it was to logon the MVM and change address in the Foundstone Configuration Agent to point to FCM server. Since this is an FS850 I would try what Jeff wrote but I'm pretty sure you will probably have to re-image the appliance.