I couldn't get this module to work so I started looking around for solutions. One thing I noticed rather quickly was that the modules documentation was telling me to put ARC2_Reader.php in modules/rdf/vendors/arc2, but the RDF modue's install instructions was telling me to put the entire ARC2 library into sites/all/modules/rdf/vendor/arc/
So after blind testing of all possibilities there and in between I have found what works best for me.
Solution
Download the ARC2 library
Extract full ARC2 library into sites/all/modules/rdf/vendor/arc/
Comments
Comment #1
febbraro commentedI removed the misleading comment. Thanks.