Yes i fixed it :)
Indeed it was the Connection string!
The correct one was (provided by the settingsfile) :
@"Data Source=(LocalDB)\v11.0;AttachDbFilename=" + _global._applicationPath
+ @"\APWarenSysDB.mdf;Integrated Security=True;Connect Timeout=30";
Well taht did it :)
To your Question digimanus : This is used once on program launch, the db connection gets then provided to all classes that need it.
But now i got an other issue :/ But i'll first try to fix it my self :)