Stack Trace:

#0 /var/www/library/IXR/Capability.php(78): IXR_Clients::query('Capability', 'user_has_cap', Array)
#1 /var/www/library/Client/Capability.php(22): IXR_Capability::user_has_cap('', NULL)
#2 /var/www/library/Webx/User.php(725): Client_Capability::user_has_cap('', NULL)
#3 /var/www/library/Webx/User.php(736): Webx_User->hasCapability('')
#4 /var/www/10676/ulmer-kalender.de/framework/application/bootstrap.php(303): Webx_User->isEditor()
#5 /var/www/10676/ulmer-kalender.de/htdocs/index.php(31): require('/var/www/10676/...')
#6 {main}