Problem with thumbnail showing using custom field

I am having a problem with the thumbnail using custom fields showing up on my home page, however if you click on the individual post it shows. https://www.reewrite.com

A tech consultant from hostgator suggested I am exceeding the alotted PHP memory useage with the timthumb.php script, and pointed me to an error, here:
https://www.reewrite.com/wp-content/themes/magazine_10/tools/timthumb.php?src=https://www.reewrite.com/wp-content/uploads/2010/08/40weeks1.jpg&h=150&w=150&zc=1

She suggested optimizing the script or upgrading to a VPS / Dedicated plan.

Can anyone speak to this? I post weekly to this blog and use a thumbnail all the time and have never ever had this problem.

Any help or advice woud be greatly appreciated.

Thanks!