I encounter this error message when trying to connect to my Oracle 8i Database.
TNS-12500 TNS:listener failed to start a dedicated server process
Cause: The process of starting up a dedicated server process failed. The executable could not be found or the environment may be set up incorrectly.
Action: Turn on tracing at the ADMIN level and re-execute the operation. Verify that the Oracle Server executable is present and has execute permissions enabled. Ensure that the Oracle environment is specified correctly in LISTENER.ORA. The Oracle Protocol Adapter that is being called may not be installed on the local hard drive. Check that the correct Protocol Adapter are successfully linked. If the error persists, contact Oracle Customer Support.
First check the database is up and running.If it is on unix OS check for the background process.If it is on NT control panel-->services the DB is started or not.If the database is up and running,try to configure the listener once again.