If we face in issue starting the Apache as below after cloning.
$INST_TOP/admin/scripts/adapcctl.sh start

adapcctl.sh: exiting with status 204

Cause:

The issue persists even after the below script is run in the Target instance, to remove references to the SSO configuration of the Source instance:

txkrun.pl -script=SetSSOReg -removereferences=yes
 
This is  due to residual references to SSO configuration in the <SID_hostname>.xml context file.

The "s_mod_osso_conf_comment" variable enables or disables mod_osso for R12. This variable is updated by the SSO registration utility for R12.

Solution:

First Fix:-
If the instance is SSO enabled the deregister SSO and register back SSO properly.Check the log file of SSO for any issues.

Start the Apache service to re-test the issue.
Second Fix:-
This variable should have a value "#" if the instance is not SSO enabled.

1. Backup the $CONTEXT_FILE.

2. Edit the parameter  "s_mod_osso_conf_comment" in the $CONTEXT_FILE using 
    editContext utility,  or manually using a text editor

3. Set the value for the above parameter to "#"
    <mod_osso_conf_comment oa_var="s_mod_osso_conf_comment"/># 
    </mod_osso_conf_comment>

4. Save the changes and run Autoconfig
    If you are facing issue while running autoconfig.The use $AD_TOP/bin/adconfig utility and 
    provide full path of the context file whihc has been updated.

5. Start the Apache service to re-test the issue