Hi there, Please try downloading the latest devel version of Rgraphviz, available here: http://www.bioconductor.org/packages/bioc/devel/src/contrib/Source/Rgraphviz_1.6.5.tar.gz I believe that Rgraphviz 1.5.10 is not compatible with graphviz 2.4 (which was not released at the time 1.5.10 was). + seth