First some background based on my experience...
When a user opens an Excel file from an Outlook email, a copy is saved in a temp directory related to Outlook.
You can test this by opening a file from an email and then choosing Save As. Note the path where Excel wants to save the file. It probably points to a temp directory on your system.
I have often "misplaced" a file that I have edited after opening it from an email because I simply clicked Save, expecting it to be saved in my Default location. In reality it was saved in a temp directory and I have to go looking for it.
Now for my hypothetical possibility:
Perhaps a link has been created in your file that points to a file that is currently saved in the user's temp directory. If an Excel file contains links to an external file that is not open on the same machine, those links will display the full path to the file so that the linked data can be retrieved.
If the user were to move that file out of his temp directory (or delete it) I believe that the links in the file you are using will break and the data will not able to be retrieved.
Does that sound like a possibility?
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