Thx for the answer. It was an User-Group setting in our Network.
But I've got another thing now. I've published a service successfully, but i'm not able not view with
the REST API (arcgis javascript). After clicking on the Service, the page is blank. Also, there is
no REST-URL in the service properties.
Do i have to change/add/install anything else in 10.1, so that the REST-API is working?