No calendar integration on iOS7 and 6

I can open a winmail.dat appointment with Klammer but cannot create a calendar entry from there, “This app does not have access to your calendars.” Unfortunately there is no setting to allow this app to use the calendar, so the main function is useless … :-(

Used equipment: iPhone 5S with iOS7.0.3 (11B511), Klammer version not visible in app, bought nov-2013.

The same issue occurred before on an iPhone 4S with iOS6 (latest version), same app.

Guzzisto about Klammer, v3.1