Strange GMail error

Got a strange GMail message that persisted with a single message.  I composed an email, and clicked on send.  Up popped the following message:

Oops... a server error occurred and your email was not sent. (#793)

It persisted.  I was able to create and send another message, and yet when I went to my drafts folder to send it again, I got the error again.

I finally solved it by closing the browser and re-signing into GMail.