Yup, FWIW, Graphviz2/IPC::Run do avoid @ARGV, so "Argument list too long" shouldn't come out of that code -- Try adding use Carp::Always; to get more info

do you do any other system/qx/``/open in the program? glob with an old version of perl?( perlfaq5#Why do I sometimes get an "Argument list too long" when I use <*>? )