Try looking in the assets/modules/txnewsletters/txnewsletters.inc.php
Around line 1731, find this line:
$link = $modx->makeUrl($modx->TXNewsletters[’idPageSubscribe’],"", "", "full").’
?&action=confirm&control=’.$MD5."&".$query;
try removing the
? before &action and see if that helps with the 404 error.
EDIT:
The above would probably work fine if you are not using friendly url’s, maybe this would work better:
find the line noted above, comment it out and add these lines in its place.
$seperator = ($modx->config['friendly_urls'] =="1") ? "?" : "&";
$link = $modx->makeUrl($modx->TXNewsletters['idPageSubscribe'],"", "", "full").$seperator.'action=confirm&control='.$MD5."&".$query;