[ERROR] Unknown authentication method: mysql:/etc/pureftpd-mysql.conf

This indicates that your build of Pure-FTPd does not include MySQL support.  MySQL support is required in order to use the Pure-FTPd MySQL module as described in our published system requirements.

To correct this problem, you'll need to do one of the following:

1. Rebuild Pure-FTPd with MySQL support, OR
2. Install the Pure-FTPd MySQL package (if one is provided by your Linux distribution -- Debian, for example, provides a pure-ftpd-mysql package), OR
3. Use the non-MySQL Pure-FTPd integration module included with Centova Cast (in the ftp/pure-ftpd/non-mysql directory).  This will allow you to integrate Centova Cast with Pure-FTPd without adding MySQL support to Pure-FTPd.

If you use CPanel on your server, you will almost certainly need to choose option #3.