The only way to diagnose this is to use the Script Editor. In the Script Editor menu "Script", check the option "Echo All Commands". In the bottom half of the Script Editor, type the command "GraphEditor" and hit the enter key on the keypad, not the regular enter next to the keys. Maya will print out everything it executes while issuing this command including any error messages. Only the last item on this list is displayed in the status bar at the bottom of the screen, so there might be more than one error message.
This is what I get (Maya 5.0):
GraphEditor;
tearOffPanel "Graph Editor" "graphEditor" true;
addGraphEditor graphEditor1;
OutlinerEdMenu graphEditor1OutlineEd;
OutlinerEdMenu graphEditor1OutlineEdSlave;
createModelPanelMenu modelPanel1;
createModelPanelMenu modelPanel2;
createModelPanelMenu modelPanel3;
createModelPanelMenu modelPanel4;
buildPanelPopupMenu hyperGraphPanel1;
buildPanelPopupMenu graphEditor1;
// Result: graphEditor1Window //
editMenuUpdate MayaWindow|mainEditMenu;
I believe most of these are mel commands which you can duplicate yourself to re-create the graph editor.
