All you will really need from your 2015 tax return is your 2015 AGI, You can retrieve your 2015 AGI by:
If you want to double check the AGI number on your tax return with the IRS to make sure that your printed copy is the same as what is on file, you can also request a transcript here: https://www.irs.gov/individuals/get-transcript If you can’t get your transcript online, you can also request one by mail.
If you still can’t resolve your e-file reject you can always print and mail your tax return(s) instead of electronic filing, you don’t need to provide your AGI to print and mail.
