To override the amount of CCA that you are claiming, click once into the total box in column 12, then select Edit > Forms Override from the top menu. You should now be able to change the amount.
I find it very frustrating that a return is not able to be e-filed when CCA is over-ridden. We should be able to have the choice, as there are times it is just wasteful, as it is not necessary to use CCA. We DO NOT NEED TO CLAIM IT, if we choose not to... SO WHY IS THIS A THING, stopping the e-file?