I-130 rejected because no date of birth

[MrBowtie]

Does anyone know what to enter for my mother's date of birth on the I-130? the year is known, but the day and month is not. I have submitted the I-130 form twice. The first time I left the entry blank, and the second I entered N/A. Both times I included a cover letter explaining we only know the year, and included a copy of documentation from her homeland showing this. Both times it was rejected with the reason of Your Alien Relative's Date of Birth field was not completed.

I would appreciate anyone's help in this matter.

Thanks