I'm not able to replicate the error that you're seeing. What add-ons do you have enabled? And what were you doing when you got the error? I mean, were you enabling a plugin?
Have you tried testing for a plugin conflict? If not, try deactivating all of your plugins except for Exchange and then see if you continue to get the error. If not, reactivate your other plugins, one at a time, to see which plugin creates the conflict.
You can also test for a theme conflict by temporarily activating one of the WordPress default themes like Twenty Thirteen to see if the error goes away.
Try testing for conflicts and then let us know how it goes. Any additional information you have would be helpful.