Internal Server Error

imagesavealpha() expects parameter 1 to be resource, boolean given

[system/library/image.php:546] imagesavealpha()
[system/library/image.php:567] Image->load()
[system/functions.php:807] Image->__construct()
[public/engine/templ.php:1209] save_image()
[public/engine/templ.php:1871] Templ->q_images()
[public/engine/templ.php:1809] Templ->parse_template()
[public/engine/controller.php:26] Templ->render()
[index.php:69] Base->run()