Here is the stack trace:

[Fri Mar 18 15:44:57 2016] [error] PHP Fatal error: Call to undefined method Project::isError() in /usr/share/tuleap/src/common/include/URLVerification.class.php on line 607, referer: https://gerrit.tuleap.net/
[Fri Mar 18 15:44:57 2016] [error] PHP Stack trace:, referer: https://gerrit.tuleap.net/
[Fri Mar 18 15:44:57 2016] [error] PHP 1. {main}() /usr/share/tuleap/plugins/tracker/www/index.php:0, referer: https://gerrit.tuleap.net/
[Fri Mar 18 15:44:57 2016] [error] PHP 2. require_once() /usr/share/tuleap/plugins/tracker/www/index.php:21, referer: https://gerrit.tuleap.net/
[Fri Mar 18 15:44:57 2016] [error] PHP 3. URLVerification->assertValidUrl() /usr/share/tuleap/src/www/include/pre.php:233, referer: https://gerrit.tuleap.net/
[Fri Mar 18 15:44:57 2016] [error] PHP 4. Tracker_URLVerification->userCanAccessProject() /usr/share/tuleap/src/common/include/URLVerification.class.php:558, referer: https://gerrit.tuleap.net/
[Fri Mar 18 15:44:57 2016] [error] PHP 5. URLVerification->userCanAccessProject() /usr/share/tuleap/plugins/tracker/include/Tracker/Tracker_URLVerification.class.php:63, referer: https://gerrit.tuleap.net/