Error The Operation Cannot Be Performed Because The Message Has Been Changed Description: The messages affected are the ones that Outlook has automatically saved a draft of while you are editing them. If you create a new message, type quickly, and send before a draft is saved.
The message will send fine; however, if you take time to compose the message and Outlook saves a draft for you, the message “The operation cannot be performed because the message has been changed” occurs when you try to send it.
The message that Outlook thinks has changed is the one in the drafts folder, and the send fails because it cannot delete the draft as part of the send operation.
After the first draft has been saved, subsequent draft saves fail, which is why some people have complained that when the draft is re-opened, it does not have the latest edits.
This Error massage applies for all versions of windows like Windows 10, Windows 8 & 8.1 and Windows 7.