Error 35

I am getting an Error 35 when trying to file my mother's taxes for 2025. She passed away in 2026 so I understood everything should be 'normal for 2025' but is this the reason I am getting the error? Also, when I print the tax forms to mail in, it is asking for a signature from her and my dad to approve the pension splitting. How do I go about that if I have to paper file?