Hi Areti,
Is it possible to run a GUI in your stage environment? because else this will not work.
jfind is a executable jar so you can just double click on it and run. On the dialog that opens, on the first text field, give the path to your jboss installation.
On the second text field give the value as "oracle.jdbc.driver.OracleDriver". Then it will show if more than one jar already contains this class file within your jboss installation.
Since you said its working fine in DEV and UAT, why not cross reference the libraries to see if they are the same.
Regards,
Dinuka