- What's a dlink?
- Your PC connects wirelessly and your sons is getting an error? That's correct?
- What is the full and exact error message? I doubt if it is "the vpn cannot be found". In fact, you're the only one that ever wrote that sentence, according to google.
- A PC wanting a vpn isn't standard. It must be setup to use a vpn. Is it? Did you? Why? Is yours also using a vpn?

Note: vpn = virtual private network. Used to call in to your companies terminal server for a safe connection so he can work at home. If that's the intention indeed, better take his PC to the companies IT-staff and let them configure it correctly.