--- nodeaccess_userreference.module
+++ nodeaccess_userreference.module
@@ -76,7 +76,7 @@
  */
 function nodeaccess_userreference_form_alter($form_id, &$form) {
   if ($form_id == '_content_admin_field' && $form['field_type']['#value'] == "userreference") {
-    $variable = 'nodeaccess_userreference_'. $form['field_name']['#value'] .'_'. $form['type_name']['#value'];
+    $variable = substr('nodeaccess_userreference_'. $form['field_name']['#value'] .'_'. $form['type_name']['#value'], 0, 48);
     $data = variable_get($variable, array('view' => 0, 'update' => 0, 'delete' => 0));
 
     $form['widget']['nodeaccess_userreference_view'] = array(
@@ -112,7 +112,7 @@
  * Extra submit function for User Reference field config.
  */
 function nodeaccess_userreference_content_field_edit_form_submit($form_id, $form_values) {
-  $variable = 'nodeaccess_userreference_'. $form_values['field_name'] .'_'. $form_values['type_name'];
+  $variable = substr('nodeaccess_userreference_'. $form_values['field_name'] .'_'. $form_values['type_name'], 0, 48);
   $data = array(
     'view' => $form_values['nodeaccess_userreference_view'],
     'update' => $form_values['nodeaccess_userreference_update'],