Uploading large files via filefields.

You need to changed the memory limit in php.ini and modify the drupal root .htaccess file to permit this

The start of the .htaccess file now looks like this. 

php_value post_max_size 51m
php_value max_input_time 2680
php_value upload_max_filesize 50m
php_value upload_tmp_dir /tmp
php_value memory_limit 110m

additional settings in php.ini 

max_execution_time,

max_input_time,

post_max_size,

memory_limit