IE8: Unable to get property 'beforeSubmit' of undefined or null reference

+++ b/clientside_validation.js
@@ -1416,7 +1416,13 @@
+        if (typeof Drupal.ajax[ajax_el].options == undefined) {

Don't you mean !=

+++ b/clientside_validation-ie8-fix-2279537-1.patch
@@ -0,0 +1,19 @@
+diff --git a/clientside_validation.js b/clientside_validation.js
+index 2268dc5..f78c449 100644
+--- a/clientside_validation.js
++++ b/clientside_validation.js
+@@ -1416,7 +1416,13 @@
+   Drupal.behaviors.ZZZClientsideValidation = {
+     attach: function () {
+       function changeAjax(ajax_el) {
+-        var origBeforeSubmit = Drupal.ajax[ajax_el].options.beforeSubmit;
++        var origBeforeSubmit;
++        if (typeof Drupal.ajax[ajax_el].options == undefined) {
++          origBeforeSubmit = Drupal.ajax[ajax_el].options.beforeSubmit;
++        }
++        else {
++          Drupal.ajax[ajax_el].options = {};
++        }
+         Drupal.ajax[ajax_el].options.beforeSubmit = function (form_values, element, options) {
+           var ret = origBeforeSubmit(form_values, element, options);
+           // If this function didn't return anything, just set the return value to true.
diff --git a/clientside_validation.js b/clientside_validation.js

did you add this block by accident, this was removed because it was causing problems

I think the problem lies within call of function changeAjax(), not in the function itself (of course: you can always add some ifs :), but this would be working around the problem, I guess).

changeAjax gets called on line 1385 with ajax_el being 'bind' and this no identifier in the DOM (as it should), but a property name coming from the prototype of Drupal.ajax. IE 8 seems to be more picky when it comes to iterating over or when evaluating these (other browsers don't seem to be startled by this...) . Catching this with hasOwnProperty() does the trick for us.

Patch attach.

Fixed in the latest dev version. Thanks for the patch!