I apologize for taking so long to resolve your issue. It really should not be this difficult to get a serial key working. It sounds like you are correctly getting the dialog box for the key to be entered. Once entered it should not show that dialog again because the .lic file is then created. I can only think that the serial key you are entering is not valid. I cannot work out which customer you are from your handle name!
Please send me an email at email@example.com
with the name you used at purchase and I will send you a new serial key that will certainly work.