--- ../MMPBSA.pypp	2012-03-29 16:52:57.000000000 +0200
+++ MMPBSA_patched.pypp	2012-04-17 14:33:26.190245000 +0200
@@ -494,7 +494,10 @@
 # Only need to find external programs if we're doing a real calculation
 if not FILES.make_mdins and not FILES.rewrite_output:
    # Find our programs and broadcast them
-   if master: external_progs = find_progs(INPUT)
+   if master:
+      external_progs = find_progs(INPUT)
+      if external_progs is None:
+         sys.exit("Not all executables for required programs have been found.")
    external_progs = MPI.COMM_WORLD.bcast(external_progs, root=0)
 
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