BuddyPress 2.0.2 is compatible with WordPress 4.0 See this site: it’s working ! 😉
500 Internal Server Error is a generic error message, given when no more specific message is suitable. There are a number of causes for a 500 Internal Server Error to display in a web browser. (cite)
Which theme do you use ?
https://wordpress.org/support/topic/500-server-error-after-upgrade-to-wordpress-40
add following line in your wp-config.php
file:
define('SCRIPT_DEBUG', true);
and activate the already existing define('WP_DEBUG', false);
to define('WP_DEBUG', true);
and feedback here.
BuddyPress 2.1 milestone estimation