What are the possibilities of getting following error.

Also is it mandatory to include hsqldb.jar in classpath and LIB folder of WEB Application ?

------------------------------------------------
6/02/07 18:22:49 CustomerEditAction...............prepareEdit()......START
et.sf.hibernate.HibernateException: Session is closed
at net.sf.hibernate.impl.SessionImpl.connection(SessionImpl.java:3327)
at net.sf.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:40)
at net.sf.hibernate.transaction.JDBCTransactionFactory.beginTransaction(JDBCTransactionFactor
.java:19)
at net.sf.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:2251)
at de.laliluna.library.bl.LibraryManager.getCustomerByPrimaryKey(LibraryManager.java:361)
at de.laliluna.library.struts.action.CustomerEditAction.prepareEdit(CustomerEditAction.java:5
)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:324)
at org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:280)
at org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:216)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:507)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at com.evermind.server.http.ServletRequestDispatcher.invoke(ServletRequestDispatcher.java:824

at com.evermind.server.http.ServletRequestDispatcher.forwardInternal(ServletRequestDispatcher
java:330)
at com.evermind.server.http.HttpRequestHandler.processRequest(HttpRequestHandler.java:830)
at com.evermind.server.http.HttpRequestHandler.run(HttpRequestHandler.java:285)
at com.evermind.server.http.HttpRequestHandler.run(HttpRequestHandler.java:126)
at com.evermind.util.ReleasableResourcePooledExecutor$MyWorker.run(ReleasableResourcePooledEx
cutor.java:186)
at java.lang.Thread.run(Thread.java:534)

without any of the code I'd guess that error came from trying to use a closed session object