To resolve the warning, copy the prefs.ora file from your Reports Builder $ORACLE_HOME/tools/admin/ directory into the Applications $HOME directory.
Copy of the file prefs.ora in the directory /sharp01/prod/apps/tech_st/10.1.2/tools/admin to the directory /home/appprod/.
Kindly provide more details, like
1. Is this issue with all the reports or a specific report.
2. If it is with a specific report was it working earlier.
3. Did anything changed on the server.