src/Tools/jEdit/src/isabelle_hyperlinks.scala

   extends AbstractHyperlink(start, end, line, "")
 {
   override def click(view: View) = {
     Isabelle_System.source_file(Path.explode(def_file)) match {
       case None =>
-        Library.error_dialog(view, "File not found", "Could not find source file " + def_file)
+        Library.error_dialog(view, "File not found",
+          Library.scrollable_text("Could not find source file " + def_file))
       case Some(file) =>
         jEdit.openFiles(view, file.getParent, Array(file.getName, "+line:" + def_line))
     }
   }
 }