REP-0004: Warning: Unable to open user preference file.

[admin]

In the log try to find the error like below,

One or more post-processing actions failed. Consult the OPP service log for details.

take the request ID and search the OPP path using following SQL,

SELECT fcpp.concurrent_request_id req_id, fcp.node_name, fcp.logfile_name
FROM fnd_conc_pp_actions fcpp, fnd_concurrent_processes fcp
WHERE fcpp.processor_id = fcp.concurrent_process_id
AND fcpp.action_type = 6
AND fcpp.concurrent_request_id = XXXXXXXXX

It will show the path of the log file so open and try to find the error. If it is not able to find appltmp (No such file or directory) then login to,

XML Publisher Administration responsibility > Tab : Administration > Configuration
Check and update the path of temp folder : Properties > General > Temporary Directory

Retest the issue as the above can happen when you clone the instance for TEST or DEV.