Here is a nice conflict between Oracle products. I installed “Oracle Database 10g Express Edition” along with “Oracle Containers 4 Java” as the application server to run my J2EE app on. I installed the database engine first and then configured OC4J. OC4J needs an environment variable called ORACLE_HOME in order to run. This needs to point to the folder where you unzipped it. Everything worked just fine at this stage .