Well at least you are in 5.1u1c. xD
What seems clear is that there is a problema with the U2 updater, so other updates work well, the only one that fails is the U2 one...
Do you have another vcenter available?? If not, you can try to do a fresh install on a vm of the U2 version and copy later the JRE folder to the problematic one. Maybe that Works for you... IS strange... do you stop all vmware services before upgrading, right???
REgards.