Tell him to check his firewall and make sure aceshigh.exe is allowed through it. If a router is causing the problems, then Aces High II uses a random subset of ports in the range of 2000-6000 for both TCP and UDP.
The easy way to test to see if a router or firewall is causing the problem for creating an account is to open a browser and then go to our main WEB page. If the browser can open it, then it is a firewall blocking the game as the account informtion is sent to the WEB server over a different port.
If the browser cannot connect to our WEB page then it is an Internet related issue which needs to be addressed with the ISP.