If you do not need to use your Tuition Credits to reduce your tax payable to zero, the amount you have entered will be carried forward and available for use when needed. 

This is not an error, TurboTax will only apply the credits if you need them. If you do not need to use them this year, nothing will show up on Line 323. You will see an amount "available to carry forward" in the Student Summary.

https://turbotax.community.intuit.ca/replies/3798733