try to testconnection in JDBC teststep, get an error

I'm using the new version soapUI3.5-beta1, and when I new a JDBC teststep, and set
driver = oracle.jdbc.OracleDriver
connection String =  jdbc:oracle:thin:kitty/kitty@127.0.0.1:1521:xe
when I click "TestConnection" button,get an error msgbox with the information as below:

"Can't get the Connection for specified properties;java.lang.NullPointerException: replacement"

I have put oracle jdbc driver jar classes14.jar into the folder bin\ext, and I can promise that my username, password, and sid all are right!

pls can give me some help?

Thank you very much

Best Regards