Apple Configurator apps

Hi everyone.

We are trying to use Apple Configurator on an iMac to manage our iPads. when we go into the "apps" section of Configurator, there are no apps in the list to start with. When we go to add some, any app that is clicked on displays this error:

Unable to import app " *app name* ". The app's identifier is missing.

Does anyone know what might be causing this and how we can get our apps out onto our iPads? Sorry if this question has already been posted, I couldn't find it anywhere.

Thanks.