Index: hierarchical_select.js
===================================================================
RCS file: /cvs/drupal-contrib/contributions/modules/hierarchical_select/hierarchical_select.js,v
retrieving revision 1.36
diff -u -p -r1.36 hierarchical_select.js
--- hierarchical_select.js	3 Mar 2008 20:25:08 -0000	1.36
+++ hierarchical_select.js	3 Mar 2008 23:51:03 -0000
@@ -174,7 +174,9 @@ HierarchicalSelect.initialize = function
     .html(this.setting(hsid, 'initial'));
     
     // Mirror the 'error' class from the original select.
-    var classes = $('select.hierarchical-select-'+ hsid +'-original-select', this.context).attr('class').split(' ');
+    var classAttribute = $('select.hierarchical-select-'+ hsid +'-original-select', this.context).attr('class');
+    classAttribute = (classAttribute != null) ? classAttribute : ''; // Work-around for Internet Explorer 6/7 compatibility. See http://drupal.org/node/229513.
+    var classes = classAttribute.split(' ');
     for (var i = 0; i < classes.length; i++) { // TODO: I'm sure this can be done cleaner!
       if (classes[i] == 'error') {
         $('select.hierarchical-select-'+ hsid +'-select', this.context).addClass('error');