Upgrading core 2.9 to latest core version 3.1: blank screen

I tried to upgrade core version 2.9.2 to 3.1.2. The update starts, mentioning an upgrade from indeed 2.9.2. to 3.1.2.. Clicking start update results in a blank screen with the url: http://sliderules.nl/system/index.php?C=wizard&M=do_update&language=english A previous update from 2.8 to 2.9 was succesfull. Setting $debug to 1 index.php does not provide information. All relevant files/folders are writable.

Any ideas?

In the meantime Robin Sowell found the bug in wizard.php, located in /ee/installer/controller. Line 151 should read: define(‘IS_CORE’, TRUE); for the core version.