500 Internal Server Error

oracle.apps.fnd.common.AppsException: oracle.apps.fnd.common.PoolException: Exception creating new Poolable object.

If you are getting the above error while running the page from Jdeveloper that means you have opened so many sessions and not logged out them.

For this you will have to ask DBA to kill the sessions.

Once you start running page from JDeveloper, every time log out instead of directly closing the window.