Hi @Glenn Maxwell ,
It seems that the error you are encountering is related to required properties in SharePoint. This error can occur when opening a document in Word Desktop App if there are invalid or missing required properties.
1.In order to see the actual error that is occurring. The text 'To save to the server, correct the invalid or missing required properties' is also a link. Clicking on that link will take you to 'Info' settings page.
Click on 'Show All Properties'
There you will find the exact item that is giving you the error and when you hover over the error, it should provide a little more insight into the issue so that you can save your file.
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2.Another Microsoft article provides some suggestions for fixing issues opening Microsoft 365 files and documents from SharePoint document libraries.
Some problems occur because of differences in versions of SharePoint server and Microsoft 365. If you can't get it to work, try downloading the file and seeing if you can open it locally.
3.If that doesn't work, check to see if the solution in this thread helps you, I look forward to hearing from you: https://learn.microsoft.com/en-us/answers/questions/245450/error-to-save-to-server-correct-the-invalid-missin
Hope the information can help you. And if there have any unclear or misunderstanding, please feel free to post back and we’ll continue to help you all the time!
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