According to the built-in help for the Motion Blur plug-in, the current parameters should be in the order of (run_mode, image, drawable, type, length, angle, center_x, center_y). I was thus able to make this script work by shuffling the order of the arguments.
--- usr/lib/gimp/2.0/plug-ins/glowing_steel 2005-12-21 20:34:12.000000000 -0700 +++ home/lade/.gimp-2.2/plug-ins/glowing_steel 2007-01-12 01:45:01.000000000 -0700 @@ -203,7 +203,7 @@ gimp_brightness_contrast($templ, 50, 0); plug_in_noisify($image, $templ, 0, 0.3, 0.3, 0.3, 0); - plug_in_mblur($image, $templ, 0, $length, $angle, 0.0, 0.0, 1); + plug_in_mblur(1, $image, $templ, 0, $length, $angle, 0.0, 0.0); # Now put it into the target layer gimp_selection_load($target_select);
