Encountered a situation recently where I had to reenter my product key whenever I opened a Microsoft Office 2011 application, even though my software was already licensed.
Microsoft’s support site states that the error could be triggered because the licensing file is either missing or corrupted or because the Installation ID for the license does not match the installation ID of the computer on which Office for Mac is installed.
Microsoft offers several methods for resolving this type of error. One suggestion was to move three licensing files from the Mac’s Library folder to the trash:
2011 Microsoft Office For Mac Keyboard Shortcut
Important note for Microsoft 365 subscriptions: After September 22, 2016, Office 2011 for Mac is no longer available for installation with a Microsoft 365 subscription.This doesn't affect one-time purchases of Office for Mac 2011 such as, Office Home and Student, Office Home and Business, or Office. OFFICE MAC 2011. PRODUCT KEY IS ON BACKSIDE OF CASE. ONLY WHAT IS PICTURED IS INCLUDED. OFFICE MAC 2011. PRODUCT KEY IS ON BACKSIDE OF CASE. Microsoft Office MAC 2011 Home and Business Licensed for 2 MACs =NEW RETAIL DVD= $99.95. NEW 2020 Office Suite Software-Home Student-Microsoft Windows-Mac.
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I was required to enter my admin password to trash the first two files but not the third. After I moved the files, Office 2011 would not start nor did the program ask me to enter my product key again.
Undaunted, I decided to see what would happen if I moved those same three licensing files back to their original locations (hint: Don’t empty the trash!), reentering my admin password in order to complete the process.
Microsoft Office 2011 Product Key
Voilà! Success! Office 2011 started up in a normal fashion without asking for the software product key. It is now apparent that the problem was triggered by a file permissions conflict, and by transferring the licensing files back-and-forth on my Mac, I restored permissions to their proper setting.