Form 5471 Error – “Identifying number of the Foreign Corporation is invalid”

Hi everyone,

I’m running into an EF diagnostic in ProConnect that I haven’t been able to resolve and would appreciate any guidance.

I am preparing a 2025 Form 1040 with a Form 5471 for a foreign corporation. The corporation does not have a U.S. EIN, so I selected “Foreign US” and entered a reference ID number.

However, I keep receiving the following error:
“Form 5471 #1: The identifying number of the Foreign Corporation is invalid. US - Ref #2017955”

Here’s what I’ve already tried:

Entered a valid reference ID (letters and numbers only)
Left EIN as “Foreign US”
Ensured no duplicate 5471 entries
Re-entered the form from scratch
Confirmed foreign address and country are correct
Removed any U.S. address fields

Despite all of this, the error persists and is preventing e-filing.

Has anyone encountered this issue before in ProConnect?
Is there something specific about the reference ID format or another field that could be causing this?

Any help would be greatly appreciated.

Thank you!