How to fix Signature Issue in Microsoft Excel

Dear @David Murray,

Thank you for taking the time to test that and for sharing the additional results.

I also appreciate the thorough troubleshooting you have already performed. Based on everything you've reported so far, you've now ruled out several of the most common causes:

• The issue occurs across multiple users.
• It occurs on newly created workbooks.
• The behavior is unchanged in Excel Safe Mode.
• The same certificate can be used successfully in Word.
• An Office Online Repair has already been completed without changing the behavior.

Given these findings, this appears to be more than a typical workstation, add-in, or document-specific issue. Since the problem affects multiple users following the migration to Windows 11 devices and can be consistently reproduced, I am increasingly inclined to believe that this warrants a deeper investigation than can realistically be performed through the community forum alone.

At this stage, my strongest recommendation would be to work with your Microsoft 365 administrator to open a Microsoft support ticket and provide the collected details.

Since this issue is affecting users who need to sign Excel workbooks as part of their work, I would recommend moving this to a formal Microsoft support ticket rather than continuing with only community-level troubleshooting. This will give your organization access to the right diagnostic tools and escalation path and should help reduce the risk of further disruption to your users’ work.

The information you have already gathered should be very useful for support, especially the Excel diagnostic logs containing the -2147418113 (E_UNEXPECTED) error, the Office build information, the certificate template details, and confirmation that Word can sign successfully while Excel cannot.

You can raise support ticket from Microsoft 365 Admin Center>Support>Help & Support.  

For reference:  Get support | Microsoft Docs   

Thank you again for the detailed testing and for sharing your findings with the community. You have already completed many of the troubleshooting steps that would normally be requested, and the information you've gathered should provide a strong starting point for a formal investigation.

If this response has helped you better understand why this issue may require deeper investigation beyond general troubleshooting, please consider marking it as the Accepted Answer.

Doing so will help other administrators and IT support teams who may encounter similar Excel signature issues after moving to Windows 11 or deploying new Microsoft 365 Apps builds. It also makes the thread easier to find for users searching for related symptoms such as Excel signature line failures, certificate signing issues, or the E_UNEXPECTED error.

Thank you again for sharing your detailed test results. I hope your organization is able to receive the right support and resolve this with minimal disruption to your users’ work.

Kind regards.

Dear @David Murray,

I hope you’re having a good day.

Thank you for providing such a detailed description of your environment and the troubleshooting work you have already performed.

One detail that stands out is that the same certificate can be used successfully to sign signature lines in Word, but not in Excel. This suggests that the certificate itself is at least being recognized by Microsoft 365 Apps and may help narrow the investigation toward an Excel-specific issue, certificate provider interaction, add-in interference, or an environment change introduced during the Windows 10 to Windows 11 migration.

As initial troubleshooting, I would recommend the following checks:

1. Test with a new workbook
   • Create a brand-new Excel workbook.
   • Insert a new signature line.
   • Attempt to sign it using the same certificate.
   This helps determine whether the issue is specific to a particular workbook or affects all Excel documents.
2. Confirm whether the issue affects multiple users If multiple users with newly issued certificates on Windows 11 experience the same behavior, this may indicate an environmental or application-level issue rather than a single user profile problem.
3. Start Excel in Safe Mode
   • Press Window + R and run: excel /safe
   • Then attempt to sign the workbook again.
   If signing succeeds in Safe Mode, an Excel add-in or extension may be interfering with the signing process. Similar troubleshooting is commonly recommended when isolating Excel-specific functionality issues.
4. Temporarily disable Excel COM Add-ins
   • File > Options > Add-ins
   • Manage: COM Add-ins > Go
   • Disable non-Microsoft add-ins and test again. Add-ins are a known cause of some Excel-specific signing failures.
5. Verify the certificate Open certmgr.msc. Confirm the certificate:
   • Is present in Current User > Personal > Certificates.
   • Has not expired.
   • Includes an associated private key.
   • Is trusted by the device.
   Microsoft's documentation confirms that digital signatures rely on a valid signing certificate issued by a trusted authority.
6. Perform an Online Repair of Microsoft 365 Apps Since Word works while Excel does not, an Online Repair may help rule out an application-specific installation issue.

If the issue persists after the steps above, could you let me know the results of these tests?

• Does the failure occur for all users or only specific users?
• Does it occur in a newly created workbook?
• Are Smart Cards or hardware-backed certificates involved?
• Is the certificate template configured for document signing?
• Does the behavior change when Excel is run in Safe Mode?

Please understand that our initial response does not always resolve the issue immediately. However, with your help and more detailed information, we can work together to find a solution.  

Looking forward to hearing back from you with any updates or additional details. 

Warm regards, 

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