Looks like that the connection is not accepted by the DB.
Caused by: java.sql.SQLException: The application requester cannot establish the
connection. (Connection refused: connect)
at com.ibm.as400.access.JDError.throwSQLException(JDError.java:528)
Maybe your connect parameter are wrong.
Could you connect via JDBC with other programs. You might use SQirreL for a simple test