issue activating Microsoft Excel on a Mac running macOS Catalina 10.15.8

Michael Simpson 0 Reputation points
2026-10-15T08:24:12.0666667+00:00

We are experiencing an issue activating Microsoft Excel on a Mac running macOS Catalina 10.15.8, and would appreciate your assistance.

 

Details of the issue:

  • Operating system: macOS Catalina 10.15.8
  • Excel version: 16.66
  • Error message: Unknown Error 0x0 when attempting to activate Excel
  • Account: Microsoft 365 work account

 

We have confirmed that the user can sign in to their Microsoft 365 account and access Excel online successfully. However, when attempting to activate the desktop version of Excel, the activation process fails with error code 0x0.

We understand that Excel 16.66 is the last version compatible with macOS Catalina. The Mac cannot be upgraded to a newer version of macOS, so installing a newer version of Excel is not currently an option.

We would like to establish whether this issue is related to recent changes to Microsoft's Office activation or licensing requirements, and whether there is a supported way to activate Excel 16.66 on macOS Catalina.

 

Could you please advise on the following?

  1. Is Excel 16.66 still able to be activated on macOS Catalina 10.15.8?
  2. If activation is affected by recent licensing changes, is there a workaround or supported alternative for users who cannot upgrade their operating system?
  3. Are there any specific troubleshooting steps we should follow for this error beyond reinstalling Office or clearing local licence and sign-in credentials?

 

We would appreciate a clear explanation of the available options, as we would ideally like to continue using the desktop version of Excel without needing to replace a functioning laptop which was working fine with excel last week.

Microsoft 365 and Office | Excel | For business | MacOS
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  1. Julie Huynh 3,940 Reputation points Independent Advisor
    2026-10-15T08:42:35.53+00:00

    Hi @Michael Simpson ,

    First of all, I would like to clarify that this is a forum where users help one another by offering useful advice to those facing difficulties. Regarding your issue,

    I regret to inform you that your version of the Mac operating system is no longer supported by Microsoft for running Office applications. The current solution is to switch to a device with an operating system that meets Microsoft’s requirements, or to use the web-based version of Office.

    User's image

    You can refer this article for your reference: Update Microsoft 365 or Office on your macOS or iOS device | Microsoft Support

    Kindly let me know when there are updates or if you need further assistance.

    I'm here and happy to help! Thank you for your kindness and patience! 

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