PHP error when trying to upload images. Help!

I’ve never had any trouble when uploading images in WordPress but now I’m getting the following errors:

Warning: imageantialias(): supplied argument is not a valid Image resource in /home/content/b/e/n/benkessler/html/wp-admin/includes/image.php on line 44

Warning: Division by zero in /home/content/b/e/n/benkessler/html/wp-admin/includes/image.php on line 64

Warning: imagecreatetruecolor(): Invalid image dimensions in /home/content/b/e/n/benkessler/html/wp-admin/includes/image.php on line 68

Warning: Cannot modify header information – headers already sent by (output started at /home/content/b/e/n/benkessler/html/wp-admin/includes/image.php:44) in /home/content/b/e/n/benkessler/html/wp-includes/pluggable.php on line 390

Can anyone help?