‘Error in the application’ when configuring incoming e-mail on a list

When you try to configure incoming email on a list, you might receive the error ‘Error in the application’ when the ‘Central Admin’ application pool user differs from the ‘Web Application’ application pool user.

There might be other causes for the same symptom. For more information, see http://blogs.technet.com/jks/archive/2009/03/04/3209136.aspx