can’t upload images

When I try to upload an image into a post or page I get this error…

Warning: imageantialias(): supplied argument is not a valid Image resource in /home/.zwindler/dhammers/activedarkchocolate.com/wp-admin/includes/image.php on line 44

Warning: Cannot modify header information – headers already sent by (output started at /home/.zwindler/dhammers/activedarkchocolate.com/wp-admin/includes/image.php:44) in /home/.zwindler/dhammers/activedarkchocolate.com/wp-includes/pluggable.php on line 390

I checked those files and they look the same as another wordpress blog I have.