Unfortunately that will not help. The issue is almost certainly due to the DOCUMENT_ROOT not being properly determined.
Add the following to the timthumb-config.php file found here:
This is what you need to add, make sure to change the doc root accordingly:
'/my/doc/root' will be, will depend entirely on the server setup. If you go to the the Connections : Dashboard admin page and look at the the System widget; there will be a constant named CN_PATH. The doc root should be the beginning portion of that path. What I can tell you is that from the
wp-content on will NOT be part of the doc root.
Hope that helps!