--- loncom/homework/radiobuttonresponse.pm	2011/05/27 18:40:37	1.148
+++ loncom/homework/radiobuttonresponse.pm	2011/06/07 17:27:37	1.149
@@ -1,7 +1,7 @@
 # The LearningOnline Network with CAPA
 # mutliple choice style responses
 #
-# $Id: radiobuttonresponse.pm,v 1.148 2011/05/27 18:40:37 raeburn Exp $
+# $Id: radiobuttonresponse.pm,v 1.149 2011/06/07 17:27:37 www Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -815,6 +815,9 @@ sub end_foil {
 		&Apache::lonxml::warning(&mt('Foils without names exist. This can cause problems to malfunction.'));
 		$name=$Apache::lonxml::curdepth;
 	    }
+            if ($name eq "0") {
+                &Apache::lonxml::error(&mt('Foil name [_1] is not supported. Please choose another name.','<b><tt>'.$name.'</tt></b>'));
+            }
 	    if (defined($Apache::response::foilnames{$name})) {
 		&Apache::lonxml::error(&mt('Foil name [_1] appears more than once. Foil names need to be unique.','<b><tt>'.$name.'</tt></b>'));
 	    }