Fatal error: PHP error in file /www/htdocs/w00bbb03/wcf/lib/page/CustomPage.class.php (44): Non-static method CustomPageEditor::getChildPages() should not be called statically, assuming $this from incompatible context

Information:

error message: PHP error in file /www/htdocs/w00bbb03/wcf/lib/page/CustomPage.class.php (44): Non-static method CustomPageEditor::getChildPages() should not be called statically, assuming $this from incompatible context
error code: 0
file: /www/htdocs/w00bbb03/wcf/lib/system/WCF.class.php (255)
php version: 5.5.38-nmm3
wcf version: 1.0.11 pl 4 (Horizon)
date: Wed, 26 Jul 2017 08:29:55 +0000
request: /
referer:

Stacktrace:

#0 /www/htdocs/w00bbb03/wcf/lib/page/CustomPage.class.php(44): WCF::handleError(2048, 'Non-static meth...', '/www/htdocs/w00...', 44, Array)
#1 /www/htdocs/w00bbb03/wcf/lib/page/AbstractPage.class.php(74): CustomPage->readData()
#2 /www/htdocs/w00bbb03/wcf/lib/page/CustomPage.class.php(74): AbstractPage->show()
#3 /www/htdocs/w00bbb03/wcf/lib/page/AbstractPage.class.php(36): CustomPage->show()
#4 /www/htdocs/w00bbb03/wcf/lib/util/RequestHandler.class.php(63): AbstractPage->__construct()
#5 /www/htdocs/w00bbb03/wcf/lib/util/RequestHandler.class.php(91): RequestHandler->__construct('Custom', Array, 'page')
#6 /www/htdocs/w00bbb03/index.php(8): RequestHandler::handle(Array)
#7 {main}