The credit is non-refundable, meaning that if you owe no tax because of other deductions and credits, the adoption credit can't be used to increase your refund. It can be carried forward and applied to your tax in the future. It sounds like the Turbotax messaging is not clear on why the credit is not useable this year. (Sometimes the main screen is not helpful but there is a small blue link that says something like "why is this" or "explain more" that would explain this is a non-refundable credit.)
