Hey, I responded to your email, but I'll respond here too, in case anybody else is having this problem.
If you're ever having trouble registering your game, the ultimate fail-safe is to add it to the registry yourself. To do that, press [Windows]+[R] on your keyboard to open the "Run..." screen and run "regedit".
When regedit opens, navigate to the following folder:
HKEY_CURRENT_MACHINE\SOFTWARE\Longbow Digital Arts\Hegemony Philip of Macedon
(If you don't see that folder, you can right-click on the parent folder and choose New->Key to create it.)
Now, in the right-hand panel, right-click and choose New->String Value and name the string "Serial". Then double-click on it and set its value to whatever your serial code is.