A TimThumb error has occured The following error(s) occured: wordpress iis

step 1->go to  timthumb.php

I was able to fix my issue by doing TWO things.

I turned this line to true: [line 33]

if(! defined('ALLOW_ALL_EXTERNAL_SITES') ) define ('ALLOW_ALL_EXTERNAL_SITES', TRUE); // Less secure.

and I commented out this line [line 212]
//$this->src = preg_replace('/https?:\/\/(?:www\.)?' . $this->myHost . '/i', '', $this->src);

Whether or not this is an appropriate way, it is the fix I found to work after 8+ hours of troubleshooting.

Hopefully this helps some people!

Source: http://www.binarymoon.co.uk/2009/10/timthumb-wordpress-mu/