Hello Birgit,
Please have a look on the below links, may be useful -
http://scn.sap.com/thread/1447920
http://scn.sap.com/thread/3299124
http://scn.sap.com/thread/416848
http://scn.sap.com/thread/334423
https://scn.sap.com/thread/2047835
https://scn.sap.com/thread/1703866
https://scn.sap.com/thread/212244
https://scn.sap.com/message/10897862
From RBEI,
Snehal