i downloaded halo for my macbook and i installed it and entered the product key everything was running fine until as soon as i completed the first mission it automatically closes the programme on my laptop. does anyone know if its something wrong with the product key (which i have tried about 5 now all dont work) or do i need to change some settings?
ps i didnt buy it as it costs like £100 for a mac copy from ebay

Since you used a serial from online someone else probably used the same serial which the game recognized and 2 people can't use the same serial number.

Try using a new one but make sure you aren't connected to the internet so it cant communicate to see if that serial is a being used.