make sure that the webassist/email/waue_confirm_1.php page is not set to be read only, if that file has become read only, it will not allow for changes to be written to it.
I see a problem in the to address at line 510:
$RecipArray[$CurIndex ][] = "".(WA_getSavedFormValue("","First_Name")) ."|WA|".(WA_getSavedFormValue("","Email_Address")) ."";
that code should be:
$RecipArray[$CurIndex ][] = "".(WA_getSavedFormValue("CheckoutWizard_Sharp_Default","First_Name")) ."|WA|".(WA_getSavedFormValue("CheckoutWizard_Sharp_Default","Email_Address")) ."";
I have tried to reproduce that code error by making an edit to the server behavior, but cannot.