Keys from 4.x won't work on 5.x.
If you have an active Support/Subscription contract, you can simply upgrade your vSphere 4 licenses to vSphere 5 licenses in MyVMware, see:
Keys from 4.x won't work on 5.x.
If you have an active Support/Subscription contract, you can simply upgrade your vSphere 4 licenses to vSphere 5 licenses in MyVMware, see: