undefined constant REQUIREMENT_ERROR

After install and visiting the page "admin/config/messaging/settings" I get the following error message:

• Notice: Use of undefined constant REQUIREMENT_ERROR - assumed 'REQUIREMENT_ERROR' in messaging_requirements() (regel 494 van /Applications/MAMP/htdocs/mediation-2012/sites/all/modules/messaging/messaging.module).
• No sending method plug-ins available. Please enable some Sending Method on the Modules administration page.

After enabling a Sending Method as suggested the error message doesn't show anymore.