Warning: imagecreatefrompng

After loading and encoding video takes off error :
* warning: imagecreatefrompng() [function.imagecreatefrompng]: gd-png: fatal libpng error: [00][00][00][00]: unknown critical chunk in /usr/home/sashka/public_html/mysite.com/public/includes/image.gd.inc on line 190.
* warning: imagecreatefrompng() [function.imagecreatefrompng]: gd-png error: setjmp returns error condition in /usr/home/sashka/public_html/mysite.com/public/includes/image.gd.inc on line 190.
* warning: imagecreatefrompng() [function.imagecreatefrompng]: 'sites/default/files/videos/19' is not a valid PNG file in /usr/home/sashka/public_html/mysite.com/public/includes/image.gd.inc on line 190.
* warning: imagecreatefrompng() [function.imagecreatefrompng]: gd-png: fatal libpng error: [00][00][00][00]: unknown critical chunk in /usr/home/sashka/public_html/mysite.com/public/includes/image.gd.inc on line 190.
* warning: imagecreatefrompng() [function.imagecreatefrompng]: gd-png error: setjmp returns error condition in /usr/home/sashka/public_html/mysite.com/public/includes/image.gd.inc on line 190.
* warning: imagecreatefrompng() [function.imagecreatefrompng]: 'sites/default/files/videos/13' is not a valid PNG file in /usr/home/sashka/public_html/mysite.com/public/includes/image.gd.inc on line 190.
* warning: imagecreatefrompng() [function.imagecreatefrompng]: gd-png: fatal libpng error: [00][00][00][00]: unknown critical chunk in /usr/home/sashka/public_html/mysite.com/public/includes/image.gd.inc on line 190.
* warning: imagecreatefrompng() [function.imagecreatefrompng]: gd-png error: setjmp returns error condition in /usr/home/sashka/public_html/mysite.com/public/includes/image.gd.inc on line 190.
* warning: imagecreatefrompng() [function.imagecreatefrompng]: 'sites/default/files/videos/9' is not a valid PNG file in /usr/home/sashka/public_html/mysite.com/public/includes/image.gd.inc on line 190.