- kb.vmware.com/kb/2006859
Fresh install? If you're running 5.0 have you applied update 04?
Are you running ESXi 5.0 Update 4?
but in interoperability it shows as 5.0 U 1 and U2 and also supported
Per the KB we both mentioned, Update 4 is the point where Windows 8 and Server 2012 became fully supported. I would try patching to update 4 and see if that helps.