Error 35 and Error 51

[agm]

Trying to submit my parents taxes and getting 2 errors. For my dad it is giving me error 51 when I try to submit his taxes and my mom error 35 when I am trying to submit hers. 

I have never had or seen this issue in the past.

Has anyone experienced this before? Not sure what I have done wrong?

Thank you

[Curmudgeon]

These are the efile error codes. They might be related.

https://www.canada.ca/en/revenue-agency/services/forms-publications/publications/rc4018/chapter-2.html