How to fix REP-0004 Error: Unable to Open User Preference File

Issue faced:
REP-0004: Warning: Unable to open user preference file

SYMPSTOMS:
Concurrent request logfiles have the below error:
REP-0004: Warning: Unable to open user preference file

Cause:
The prefs.ora is either missing or non-accessible.

Solution:

1. No prefs.ora file in HOME directory:
   Oracle Reports will search for the prefs.ora preferences file in the user’s HOME directory. You can copy the prefs.ora file included with the Oracle Tools if there isn’t one in your HOME directory.
   A prefs.ora file is shipped with the Oracle Tools, and is located in:

$ORACLE_HOME/tools/admin/prefs.ora

Copy the prefs.ora file from $ORACLE_HOME/tools/admin/ directory into the Application users $HOME directory.
[TEST@ebsdb ~]$ cd /u01/ebsapps/apps/tech_st/10.1.2/tools/admin/

[TEST@ebsdb admin]$ ls

prefs.ora prefs.ora.bak prefs.ora.1 prefs.ora.2 prefs.ora.3 prefs.ora.4 prefs.ora.5 prefs.ora.6 prefs.ora.7 prefs.ora.8

[TEST@ebsdb admin]$ cp -rfv prefs.ora /home/appltest/

The prefs.ora file has insufficient privileges:
The user invoking Oracle Reports must have read privileges on the prefs.ora file.

[TEST@ebsdb ~]$ ls -ltr prefs.ora
-rw-r–r–. 1 appldev oinstall 2080 Feb 11 2016 prefs.ora

A system error made it impossible to open the file.
The preferences file may have become corrupted. If you suspect file corruption, copy $ORACLE_HOME/tools/admin/prefs.ora and reenter your preferences.

Note: Oracle Forms and Oracle Graphics also read prefs.ora, thus you will have to reenter all preferences that were set in the corrupted prefs.ora file.