There is no directory with the name "vendor" in RDF...
My report says:

ARC2 is not available. It is recommended that you install this library in order to enable support for more RDF formats and for SPARQL queries. To install, download the latest version of the library and unzip it to sites/all/modules/rdf/vendor/arc2/ under the Drupal directory. For more information please refer to the handbook.

what can I do to solve that problem?

Jens Arne