Should my (self-employed) spouse still owe provincial income tax, when he has unused tuition provincial tax credits that are available to transfer to me?

He has student amounts from previous years, but still owes tax. Turbotax makes it possible for him to transfer these amounts to me, but I understood that he had to use all the credits himself to take his tax owing to zero before he would be able to transfer any credits to a spouse. The amount owing is CPP, in case that is why....