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The workaround I’ve used to date has been to do a ‘save as’ and save the document with a slightly different file name.
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I’m not sure how widespread this problem is, but I’ve seen it a few times, and one of my work colleagues gets it regularly:
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Note (3 July 2020): This is an updated version for Word 365 (for Windows) of the original post for Word 2007 ( ).
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