Scenario:

Encountered the following error in Apps Front end while trying to access concurrent program logs/Output files which are generated before switch over.

Error:
An error occurred while attempting to establish an Applications File Server connection with the node FNDFS_STBYAPP2. There may be a network configuration problem, or the TNS listener on node FNDFS_STBYAPP2 may not be running. Please contact your system administrator.

Reason:

The log and output file is pointing to the DR Apps Node, As it was generated during the DR was Primary.  But the current log and ouput files has no issues in viewing.

Solution:

Update the node name for Log and Output files with current App server Node Name

select count(*) from fnd_concurrent_requests where LOGFILE_NODE_NAME  = 'STBYAPP1';
update fnd_concurrent_requests set LOGFILE_NODE_NAME = 'PRIMAPP1' where LOGFILE_NODE_NAME  = 'STBYAPP1';

select count(*) from fnd_concurrent_requests where LOGFILE_NODE_NAME  = 'STBYAPP2';
update fnd_concurrent_requests set LOGFILE_NODE_NAME = 'PRIMAPP2' where LOGFILE_NODE_NAME = 'STBYAPP2';

select count(*) from fnd_concurrent_requests where OUTFILE_NODE_NAME = 'STBYAPP1';
update fnd_concurrent_requests set OUTFILE_NODE_NAME = 'PRIMAPP1' where OUTFILE_NODE_NAME = 'STBYAPP1';

select count(*) from fnd_concurrent_requests where OUTFILE_NODE_NAME = 'STBYAPP2';
update fnd_concurrent_requests set OUTFILE_NODE_NAME = 'PRIMAPP2' where OUTFILE_NODE_NAME = 'STBYAPP2';