diff -r a2f2981df9b0 -r 96b242e4c59d plcopen/structures.py
--- a/plcopen/structures.py	Wed Sep 25 11:50:40 2013 +0200
+++ b/plcopen/structures.py	Fri Sep 27 16:22:40 2013 +0200
@@ -42,8 +42,10 @@
 
 ScriptDirectory = os.path.split(os.path.realpath(__file__))[0]
 
-StdBlockLibrary = LoadProject(os.path.join(ScriptDirectory, "Standard_Function_Blocks.xml"))
-AddnlBlockLibrary = LoadProject(os.path.join(ScriptDirectory, "Additional_Function_Blocks.xml"))
+StdBlockLibrary, error = LoadProject(
+    os.path.join(ScriptDirectory, "Standard_Function_Blocks.xml"))
+AddnlBlockLibrary, error = LoadProject(
+    os.path.join(ScriptDirectory, "Additional_Function_Blocks.xml"))
 
 StdBlockComments = {
     "SR": _("SR bistable\nThe SR bistable is a latch where the Set dominates."),