The trouble might be that you have installed the demo version of the app, available through the Play Store. You can’t install more than one instance of the same mobile app on a mobile device. Check that the demo version of the Mobilengine mobile app isn’t still installed on your device, and make sure that you remove it before you try to install the developer version of the app.

The other reason might be that you haven’t allowed apps from unknown sources to be installed on your Android device.
If you’re having problems installing the mobile app, refer to our tutorial on the topic, or contact our support staff.