Fix from here: http://forums.whirlpool.net.au/archive/1978519#r35738525 via http://communities.vmware.com/thread/419232
Using the 2012 box you're trying to install vCenter 5.1 on, go to HKLM\System\CurrentControlSet\Services\vpxdOpen the DependOnService key and remove ProtectedStorage from the listEnsure the vCenter Server and WebMgmt services are using domain logonsRebootStart the vCenter Server service - will take a bit, but will workRe-run JUST the vCenter install for it to complete successfully I spent several head-scratching hours trying to figure this out, now working like a charm.
Using the 2012 box you're trying to install vCenter 5.1 on, go to HKLM\System\CurrentControlSet\Services\vpxdOpen the DependOnService key and remove ProtectedStorage from the listEnsure the vCenter Server and WebMgmt services are using domain logonsRebootStart the vCenter Server service - will take a bit, but will workRe-run JUST the vCenter install for it to complete successfully I spent several head-scratching hours trying to figure this out, now working like a charm.