Thank you Saguaros! I uninstalled the component and it fixed the error message.
Curious, before the fix I also enabled debug mode (Global Configuration) and though it clearly showed up on most pages at the bottom of the screen, whenever I sent a message only the error message appeared (and no debug panel at the bottom). I'm using Chrome.
Did you see the debug-info somewhere else, or did the debug-panel actually show up on your error message page?