Hard to say what's wrong with that amount of information. But JBoss AS 6.0.0.Final is a really old and outdated version. I recommend that you try out WildFly 8 (8.2.0.Final is the latest stable one) release Downloads · WildFly.
P.S: JBoss AS has been renamed to WildFly.
Thanks for the reply , Jai. Unfortunately my client don't allow to use WildFly 8. I need to fix the issue in JBossAS6.0.0 only. I have removed defaulDS dependency from many files to remove some errors and atlast getting this error.
Is there any way to disable the EJB timer ?.