If you get a message (the message text may be vague) that states you cannot connect to the database or connection is null or oracle message file is missing, the first task is to verify that the JDBC drivers are present in the ODA drivers directory.
Solution:
Verify that the JDBC jar files are present in the ODA drivers directory, if this occurs within Eclipse copy the drivers to the ODA plugins directory within the Eclipse install path. If you find this error when viewing the application through tomcat then verify that the drivers have been copied by the client.birt build target which is executed from the BIContent directory.