If you specify that you have an external motor controller, then go to the "Motors" tab on the "Motors and Sensors Setup" screen, the "Type" drop down will be prefilled with "12V Motor (TETRIX)". If you click the drop down list box, you will notice that there is no option for "12V Motor (TETRIX)". If you select one of the other options, like "No Motor", you will never be able to specify "12V Motor (TETRIX)" again. You will have to go back to the "External Controllers" tab, click "No controllers Configured", re-setup your controller, then go back to the "Motors" tab.