The worst thing about the V-RPC copy protection is that it relies on the MAC addresses of the various networking devices connected to your PC. If you have say a laptop and add a PCMCIA networking card to it, V-RPC will refuse to run with the same unlock code.
I had exactly that problem on a customer's site some time ago. Late in the evening, we encountered a problem which I already had a solution for under RISC OS. However, to be able to connect to the customer's intranet, we also needed a special networking card which was the very reason why V-RPC would refuse to start.
The new unlock code came two days later, when we already solved the problem using a different, more lengthy approach. The resulting loss of money for the two companies involved would have paid for rather a lot of copies of V-RPC.
The lesson to be learned is that if you have a turnaround time for unlocking the software you have sold of more than a few minutes, then allow the app to run un-unlocked for your worst-case turnaround time. Even Microsoft understood that with WinXP product activation, even though I am sure that they could guarantee faster turnaround times. It is a matter of respect for your customer.
The other lesson is: never rely on any piece of software to be available when you need it if it employs an unlock code scheme.