Cannot deploy because already deployed?

Oracle Application Server playing bezerk? You undeployed an application, but ran into a memory error (or another).

An error occured while undeploying the application. The evaluate phase failed. The Adapter used in the evaluate may have thrown an exception.
Resolution:
Please call Oracle support.
Base Exception:
java.lang.OutOfMemoryError
null. java.lang.OutOfMemoryError

No trace of your application, but a deployment fails with:

Deployment failed
Base Exception: J2EE application: [application_name] has already been deployed. Redeploy needs to be used to override previous deployed application.

The solution is to check whether or not all traces have indeed been removed (obviously not):

$ORACLE_HOME/dcm/bin/dcmctl listapplications -co [container]

will still show your application. If it does, remove it with the following command:

$ORACLE_HOME/dcm/bin/dcmctl undeployapplication -a [appl] -co [container] -force -d -v

You should now be able to deploy again.

The Reverse
You see your application in Enterprise Manager Console, but cannot undeploy, due to a failed deployment. Reverse situation from above:

- check $ORACLE_HOME/j2ee/[container_name]/application-deployments
- check $ORACLE_HOME/j2ee/[container_name]/applications
for directories and ear files named after your application.
- check $ORACLE_HOME/j2ee/[container_name]/config/server.xml for entries regarding your application, and remove this line.
- check $ORACLE_HOME/j2ee/[container_name]/config/default-web-site.xml for entries regarding your application, and remove this line.

Perform an opmnctl reload, and restart OEM (emctl stop iasconsole); you should now be able to deploy again.