Liferay is a portlet and web application server written in Java.

com.liferay.portal.kernel.scheduler.SchedulerException: Unable to start scheduler

This occured from 6.1.0RC to 6.1.0 against the same database, since the Quartz scheduler database schema changed significantly. Drop all of the QUARTZ_* tables from your 6.1.0RC installation, and replace them with the 6.1.0 versions. (The tables should be empty in your installation anyway.)