diff -r -u panda3d-1.8.1/panda/src/pgraphnodes/shaderGenerator.cxx panda3d-1.8.1-patch-shadergenerror/panda/src/pgraphnodes/shaderGenerator.cxx
--- panda3d-1.8.1/panda/src/pgraphnodes/shaderGenerator.cxx	2013-02-12 17:28:17.000000000 +0200
+++ panda3d-1.8.1-patch-shadergenerror/panda/src/pgraphnodes/shaderGenerator.cxx	2013-09-01 14:44:24.965821227 +0300
@@ -1158,7 +1158,8 @@
       }
     }
     const LightRampAttrib *light_ramp = DCAST(LightRampAttrib, rs->get_attrib_def(LightRampAttrib::get_class_slot()));
-    if(_auto_ramp_on) {
+    if(_auto_ramp_on && (  (_separate_ambient_diffuse && _have_diffuse) ||
+                          (!_separate_ambient_diffuse && (_have_ambient || _have_diffuse)) ) ) {
       switch (light_ramp->get_mode()) {
       case LightRampAttrib::LRT_single_threshold:
         {
Only in panda3d-1.8.1-patch-shadergenerror/panda/src/pgraphnodes: shaderGenerator.cxx~