In earlier versions of JBoss AS I would suspect that you packaged some JBoss AS JARs in your app. Not sure if that is still the case with AS 7. But it might be helpful to know what type of app you have (WAR, EAR?) and if you listed the contents of the app (for example, if it is a WAR file, run 'jar -tf xxx.war').
Also, please tell us exactly where you placed the Oracle JDBC Driver JAR file.