PHP/ZEND free image host debugging

Hello, I have a free image host called picmecca.com. It's full of images and sometimes they open correctly, but other times an error is displayed (see attached image). I need to make sure the site works fine everytime, by eliminating any internal bug, or if not the case of an internal bug, any web browser incompatibility issue that may exist. I need the site to work correctly with all web browsers, to make sure visitors never get an error like the one shown in the attached image. The site has to work fine, without producing any error. I checked the server cpanel to verify disk usage, but I could not see anything wrong. Maybe you can check for yourself because I will provide you the server's login info. Your job: to debug the site, to find the problem, and fix it, so that no errors generate when opening images. Best regards