Cannot get the import of employer-employee relationship to work
Stefan - in order to rule out it being a bug with your set up I would recommend you take an equivalent file and test on the Demo Site.

I just created a file with 3 cells

Peter | Davis | Acme

I had already created Org = Acme in http://dmaster.demo.civicrm.org/

The import ran as expected.

Acme now has an 'employee' called peter Davis