Hi all,
not sure if this any help for you but it sounds like I once stumbled accross a similar problem (Oracle 9i, Geoserver 1.3.0 PR1, no getMap result).
Have you already tried out to edit the epsg.properties file in the gt2-epsg.jar file in the WEB-INF/lib directory of the geoserver application? There you could add your Oracle srid code. You will find some hints in the wiki page:
http://docs.codehaus.org/display/GEOSDOC/Custom+projection+definition+in+Geoserver
That was how I finally got my getMap request running. It is however possible that this will cause problems in client applications.
Another alternative could be to add the epsg:2393 srid in the srid table of your Oracle DB and than update your ALL_SDO_GEOM_METADATA table and every (!) geometry in your geometry table. I myself could not try that out because of other applications using the same geometry tables.
regards,
christoph
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Christoph Ratke
Brinkstr. 14
37181 Hardegsen
email: christoph.ratke@anonymised.com