Error message:[IMAP]NO failed to create new parser: message: malformed MIME header line

I have received the following error message. What could this be due to?
[IMAP]NO failed to create new parser: message: malformed MIME header line: /9j/4AAQSkZJRgABAQEAYABgAAD/2wBDAAoHBwkHBgoJCAkLCwoMDxkQDw4ODx4WFxIZJCAmJSMg