in the webassist/email/email_templates/registration.php file, change line 15:
<?php echo($WAGLOBAL_Root_URL); ?>users_confirm.php?ID=<?php echo($row_WAATKusers['UserID']); ?>&code=<?php echo($row_WAATKusers['UserVerificationCode']); ?>
to:
<?php echo($WAGLOBAL_Root_URL); ?>users_confirm.php?ID=<?php echo( $_SESSION["UserID"]); ?>&code=<?php echo($_SESSION['randomConfirm']); ?>
all of the available documentation for Power Messenger is available on the Power Messenger support page:
powermessenger/
when you create a mailing group, there is a "Get Signup Form HTML" button, use that signup for in your site to allow visitors to sign up for mailing groups.