Grad students are not eligible for the AOTC. But are eligible for the non-refundable Lifetime Learning Credit (LLC) or the Tuition and Fees Deduction (TFD).
If you are eligible, you have answered something wrong, in the interview. But, some people are just not eligible. There is a lower income threshold for the LLC and TFD. So even though your income was low enough to get the AOTC for your daughter's ed, it may be too high for your spouse's ed. See
https://www.irs.gov/individuals/llc
https://www.irs.gov/pub/irs-pdf/f8917.pdf
