in the waue_checkout_success_11.php file, do a find and replace for:
[FORMREF]
replace it with:
CheckoutWizard_NewFromBlank_Default
for example:
(WA_getSavedFormValue('[FORMREF]','Email_Address'))
should be
(WA_getSavedFormValue('CheckoutWizard_NewFromBlank_Default','Email_Address'))