Rgraphviz load problems frequently involve a mismatch between the version of graphviz installed on the user machine, compared to the version of graphviz used to build the package. Rgraphviz has a name space with useDynLib(Rgrahpviz), and an .onLoad function that checks that the versions of the installed and built graphviz match. Unfortunately, the .onLoad code is only evaluated if useDynLib succeeds, so in many cases of version mismatch users receive hard-to-interpret error messages. Are there any hooks or other solutions available to catch errors during useDynLib? Or will we have more success using library.dynam in .onLoad? Thanks in advacne Martin -- Martin Morgan Computational Biology / Fred Hutchinson Cancer Research Center 1100 Fairview Ave. N. PO Box 19024 Seattle, WA 98109 Location: Arnold Building M1 B861 Phone: (206) 667-2793