Pages,Keynote and Numbers dont work - HELP!

I really need some professional help here it seems. I try to get it here before calling the technical support. Following problem:

We have 3 ipad classes here at our school. Everything runs just fine, except for 6 devices in our recent new class that I set up 2 weeks ago. The 3 Apple Apps "Numbers, Keynote and Pages" dont work - you cant press on the plus button to create any document and it doesnt show any either. In the preference settings there is also no local storage where the documents can be safed. Dont know what to do here. I deleted one ipad and reset everything, sent the apps new to the device, still the same problem...

Everytime you want to open a document in any of the apps, it shows the error message: "com.apple.documentmanager-fehler (in german that means "error") 1. (zero) cant be opened right now. Pages could not read the file."

Does anyone know what I can do here? btw, we dont use apple ids, we have the vpp store and send all the apps via wifi to the pupils devices.

thanks very much in advance,

Andreas