pfSense » pfSense Packages

The syslog-ng package is warning about an old configuration file format. Pfsense is interpreting any warning message as an syntax error, therefore it's impossible to configure syslog-ng.

Syslog-ng syntax test failed: [2016-06-16T01:09:35.927253] WARNING: Configuration file format is too old, syslog-ng is running in compatibility mode Please update it to use the syslog-ng 3.7 format at your time of convinience, compatibility mode can operate less efficiently in some cases. To upgrade the configuration, please review the warnings about incompatible changes printed by syslog-ng, and once completed change the @version header at the top of the configuration file.;

Simple and quick fix would be to bump the syslog-ng config header to version 3.7. (Or allow the user to edit the header.)
Beside that, the actual behavior should be to treat warning messages as warnings and not as errors.