[TigerC10]

Is this your dedicated server? Your website is the only website on the box?

Are you the one that installed the webhosting application (apache/IIS)?

Do you have access to php.ini? If so, you should check the memory_limit variable in php.ini.

Also, check your php.ini extension list. Make sure that only the extensions you need (like GD) are enabled. Also, check the extension directory variable to see if it matches the PHP extension directory on the server (check to make sure all of the enabled extensions are in the extension directory).

I just did a little research and found that the Zend Optimizer has this problem thanks to some caching feature. If you're using Zend, you should contact them regarding this problem.