With 4.0.6 i did not get a 500.htm, just a blank white screen.
There are about 20 errors that start out the same as these two.
1) Too many keys
[04-Jun-2011 12:32:21] WordPress database error Too many keys specified; max 64 keys allowed for query ALTER TABLE wp_em_tickets_bookings ADD INDEX (ticket_id) made by require_once, require_once, require_once, require_once, do_action, call_user_func_array, em_init, em_install, em_create_tickets_bookings_table, dbDelta
2) Unknown column
[04-Jun-2011 12:41:20] WordPress database error Unknown column ‘event_seats’ in ‘wp_em_events’ for query ALTER TABLE wp_em_events CHANGE event_seats event_spaces int(5) made by require_once, require_once, require_once, require_once, do_action, call_user_func_array, em_init, em_install, em_create_events_table
I will try 4.0.7 when it comes out.
But if that doesnt work, i cant use 3.9.8, and i cant use 4.0.6, so please tell me what to delete (even if it means losing everything) so i can start over with a clean 4.0.x. Or, i would be more than happy to pay you for extra help to resolve this.