Third Party jars with a SBO

Recently I encountered a problem with installing a docapp containing a SBO which used some 3rd party jars. The SBO was added as a module and the two third party jars were added as references and the docapp archived.When this archived docapp was being installed on a clean content server installation, it invariably failed saying : Error while reading object file. Later after a sleepless night when the SBO module was removed from the docapp and the procedure carried out again, the docapp installation went smoothly. I am still trying to find out why this happened, but if any of you guys have any idea about this , do tell me.