Help! Redirect to showthread from private.php

[fairydust]

I am trying to write a mod to redirect to a particular thread i.e. showthread.php after I send a private message so using the private_insertpm_complete hook.

This does not work:

PHP Code:

$vbulletin->url = 'showthread.php?t=2' . $vbulletin->session->vars['sessionurl'];
eval(print_standard_redirect('This is my message', false, true)); 


Yet I can view the thread when I manually paste the Url into the address bar of my website.

However

This redirect does work

PHP Code:

$vbulletin->url = 'index.php' . $vbulletin->session->vars['sessionurl'];
eval(print_standard_redirect('This is my message', false, true)); 


Any suggestions as to why it does not redirect to the showthread.php URL??