Hi @onorClarke-9237,
What's the version of your Outlook(File>Office account>About Outlook)?
Receiving the above error message when sharing calendars on outlook.
How did you share your calendar to others? Was the user who you would like to share external or internal?
According to the screenshoot in your post, there seems to only be a blank box. In order to further confirm your issue, could you please provide us with your detailed errors and more information about your issues?
As Andy mentioned, that is a known issue list and you could try to check if your issue also in here, if you still need further assistance, please feek free to post back.
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