I believe that there is a bug in graph-formatting.lisp where a graph, if it gets > 10 deep, will cause adjust-array to be called to create new array entries initialized to nil instead of to zero, meaning that comparisons cause a crash. Here's a patch. Will someone familiar with this code please vet it and apply it if appropriate? Thanks, Robert Index: graph-formatting.lisp =================================================================== RCS file: /project/mcclim/cvsroot/mcclim/graph-formatting.lisp,v retrieving revision 1.14 diff -u -F^(def -r1.14 graph-formatting.lisp --- graph-formatting.lisp 23 Apr 2005 20:02:01 -0000 1.14 +++ graph-formatting.lisp 13 May 2005 02:33:33 -0000 @@ -312,7 +312,7 @@ (defmethod layout-graph-nodes ((graph-ou (walk (node depth) (unless (graph-node-minor-size node) (when (>= depth (length generation-sizes)) - (setf generation-sizes (adjust-array generation-sizes (ceiling (* depth 1.2))))) + (setf generation-sizes (adjust-array generation-sizes (ceiling (* depth 1.2) :initial-element 0)))) (setf (aref generation-sizes depth) (max (aref generation-sizes depth) (node-major-dimension node))) (setf (graph-node-minor-size node) 0)