WebAPI - error message "An error has occurred."

If you get the following error message when using WebAPI:

{ "message": "An error has occurred." }  

Try setting CustomErrors mode="Off" in your web.config.  For some reason when CustomErrors are turned on, the error message is replaced with the above message.

See the following for more info:

http://stackoverflow.com/questions/13020103/webapis-messagean-error-has-occurred-on-iis7-not-in-iis-express