Hi John,
According to your description, the situation happens when sharing a specific file. Before providing suggestions, I would like to collect more information about the situation.
- Since you posted the thread under the SharePoint category, I suppose the file is stored in SharePoint. If so, I would like to confirm how you share files with other users.
Do you go to the SharePoint library in the browser, select the file and click the "Share" button to share files by the links? If not, please point it out and let us know.
- Since the situation only happens to a specific file, what if you create a copy of it, then try to share the copy with one user, does the error message appear again?
- Please take a full screenshot of this error, and then share it with us. You can click the "Insert Image" button to upload it again.

We look forward to your response. Thanks for your cooperation.
Sincerely,
George | Microsoft Community Moderator