Hi Gerd,
You will want to open Studio One and go into Studio One>Options>Locations>Sound Sets and verify that you have the correct path set. If you do, and your files are still not showing up, go to that location and double-click one of your files. If the problem persists, you may want to submit a support ticket from within your my.presonus.com account. PreSonus may need to see all of the details involved in this issue. For example, make sure that the location is set with the correct permissions to allow your user id to view them.