With NDCHost cPanel WHM Secondary MX Plugin you may get the following error from with in WHM:
Site error: the file /var/cpanel/pluginSMX/pluginSMX.class.php requires the ionCube PHP Loader ioncube_loader_lin_5.2.so to be installed by the site administrator.
Normally if you are are getting cron messages as well you should be getting an importer error with the same error message as above.
It seems that ioncube is not longer installed after some cPanel updates. The fix is simple. Run the following cPanel command
/usr/local/cpanel/whostmgr/bin/whostmgr2 --updatetweaksettings
I beleve this occurs after cpanel updates of there DNS version only.