Can somebody explain me what I have to do to make a database connection work? Get a exception and i have no idea how to fix it.

Hello,
I'm pretty new to Bonita bpm.
At the moment I'm experimenting with it, and try to discover the capabilities of it. (because it could be interesting for our research institute)
I created my first lane with a simple process, and now I want to make a database connection to my Orcale 11g Express edition database.

So I added a connector(ojdbc7.jar as db driver) with a working db URL. (tried it with the SQL Developer)
In the database access information window I have this at the driver field:
oracle.jdbc.driver.OracleDriver
and my URL:
jdbc:oracle:thin:@localhost:1521:XE
and the user information.

The query is this:
select * from getraenke

Now, if I try the connector out, I get this exception:

java.lang.reflect.InvocationTargetException
org.bonitasoft.engine.bpm.connector.ConnectorExecutionException: USERNAME=install | org.bonitasoft.engine.core.connector.exception.SConnectorException: org.bonitasoft.engine.connector.exception.SConnectorException: java.util.concurrent.ExecutionException: org.bonitasoft.engine.connector.exception.SConnectorException: org.bonitasoft.engine.connector.ConnectorException: java.lang.SecurityException: Package was already sealed with another URL: package=oracle.jdbc.driver, url=file:/home/kraemm/BonitaBPMCommunity-7.1.3/workspace/tomcat/bonita/engine-server/work/platform/bonita_engine_17562@zitpcx17328/local/PROCESS/8637592303074397449/8637592303074397449_ojdbc7.jar.jar4627430663138202486.tmp

and I have no idea what this mean nor what I have to do?!
(nobody in our IT section has any experience with Bonita yet )

If somebody can help me, I would appreciate this.

Thanks!

Btw,: I use Ubuntu 14.04 and have the latest bonita bpm version.
I use the ojdcb7 driver.

Edit:
Okay, I did this:
http://documentation.bonitasoft.com/database-configuration-1

And that seems to be the problem. I reinstalled Bonita and tomcat was running.
After I followed these steps for a Orcale connection, it did not work anymore.

I always get the error message, that Tomcat maybe is running in a other instance, so it cant be started.
I cant even acces to the default localhost page.

I have no idea what Im doing wrong.