Adjustment of Status - I-485

Hello guys, I urgently need your help. I have been a silent reader on this forum. I just received an RFE for I-485 and it's about the I-864, affidavit of support. I used a sponsor since i don't earn enough and my wife is unemployed. On the form, my sponsor indicated she is the only joint sponsor and I submitted all the required evidences with I-864 form. However this is what I received from uscis:

Form I-864, Affidavit of Support, was submitted; however, it was not from the petitioner/sponsor. Submit a completed and signed form I-864, (revision date of 07/02/2015), for the petitioner/sponsor listed on form I-130 or form I-129F. Even if a joint sponsor will be used, the petitioner/sponsor must submit form I-864. Also, provide copies of the petitioner/sponsor's most recent federal income tax returns and all supporting tax documents (W-2s, 1099s, form 2555, and tax schedules).

Has anyone ever experienced this? Please share your thoughts and explanations! Thanks for your responses!