The CRA's "Error 35" (often specifically Result Code 35) is the software's way of saying, "This return cannot be sent electronically."
Even though your mother was alive for all of 2025, once the CRA is notified of a death (which likely happened when the 2026 death certificate was issued or CPP was notified), her Social Insurance Number (SIN) is "flagged" in their system.
You cannot use NETFILE (electronic filing) for a deceased person's return.
The CRA requires a physical signature from the legal representative (executor) to authorize the filing, and their automated system for individuals isn't set up to verify that authority electronically for a deceased SIN.
As the executor or legal representative, you (or whoever is the legal executor) must sign the return on her behalf.
You should sign as "[Your Name], Executor for the Estate of [Mother's Name].
Important: Ensure the CRA has a copy of the will or the Form RC4649 (Legal Representative Agreement) on file. If they don't, they won't process the return you sign.
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