When you regenerate the autoloads via the command line your class eZSplash should have been added to var/autoload/ezp_extension.php
Check that file to make sure that it is actually present in there.
In regard to the fatal error when trying to regenerate from the web interface, check your apache error logs rather than the ez publish logs and you should find what php error caused that fatal error. Let us know what it is.
Thanks for your reply! My class has not been added to var/autoload/ezp_extension.php and i just checked my apache error logs. There's nothing interesting in there..
Try php bin/php/ezpgenerateautoload.php -e to generate the autoloads for the extensions. Then check to see that your class has been added to var/autoload/ezp_extension.php - if not check the file permissions of the php file with that class definition and make sure it is readable by the user running the ezgenerateautoload.php script. Also make sure that var/autoload/ezp_extension.php is writeable by that user.