If you receive this webserver-error while querying the horde website
[core:notice] [pid 18909:tid 34391285760] AH00052: child pid 18911 exit signal Bus error (10)
it is an error in the processing of the horde *.php files, which often cause the killing of the webserver-process. For example, check if you use an supported PHP-Version. Further check the PHP error logfile for more details.