The tuition credit is non-refundable. So if your taxes owing are Zero, or you have a refund, then you would not be able to use the transferred tuition.

i have this same issue and this answer is not the case with me. I transfered money from my daughters tuition last year and turbo tax does not allow me to transfer this year. Doing the form manually for my daughter and from the person who did her taxes, we can transfer more than $6000 but turbo tax is reading it as 0.