I get similar errors in my error_log in php when users are uploading their files
PHP Warning: POST Content-Length of 11933650 bytes exceeds the limi
Try pasting this to .htaccess and it should work.
php_value post_max_size 2000M php_value upload_max_filesize 2500M php_value max_execution_time 6000000 php_value max_input_time 6000000 php_value memory_limit 2500M