Recently, while applying a patch on an Oracle 12c (12.2.0.1) database on Windows, I ran into a frustrating issue: datapatch kept failing with cryptic errors. D:\oracle\product\12.2.0\dbhome\bin>D:\oracle\product\12.2.0\dbhome\OPatch\datapatch -verbose SQL Patching tool version 12.2.0.1.0 Production on Fri Sep 12 09:11:37 2025 Copyright (c) 2012, 2021, Oracle.  All rights reserved.   Log file for this invocation: D:\oracle\product\12.2.0\dbhome\cfgtoollogs\sqlpatch\sqlpatch_5332_2025_09_12_09_11_37\sqlpatch_invocation.log   Connecting to database... Connection using O/S authentication failed. Enter userid that can connect as SYSDBA: sys Enter password for sys: Connecting to database...OK   catconInit failed, exiting   Please refer to MOS Note 1609718.1 and/or the invocation log D:\oracle\product\12.2.0\dbhome\cfgtoollogs\sqlpatch\sqlpatch_5332_2025_09_12_09_11_37\sqlpatch_invocation.log for information on how to resolve the above errors. After verifying the logs pointed to catcon.pl and sqlpatch_catcon_*.log,  the real culprit turned out to be something deceptively simple — the wrong SQL*Plus version was being used. SQL*Plus: Release 10.1.0.5.0 - Production ORA-12560: TNS:protocol adapter error SP2-0640: Not connected     This was strange because I was patching a 12.2 database — why would it use a 10.1 client? Root Cause:- On Windows, datapatch invokes SQL*Plus internally via catcon.pl. It will pick up the first sqlplus.exe it finds in the system PATH.To verify this I ran in cmd D:\oracle\product\12.2.0\dbhome\bin>where sqlplus D:\oracle\product\12.2.0\dbhome\bin\sqlplus.exe  ← correct (12.2) D:\oracle\developer\BIN\sqlplus.exe  ← wrong (10.1, Oracle Developer 10g)   Since the Developer 10g client was earlier in the PATH, datapatch tried to use that. And of course, a 10g SQL*Plus cannot talk to a 12c database.Solution:-1. Quick Fix (per session) Run these commands in your Command Prompt before executing datapatch: set ORACLE_HOME=D:\oracle\product\12.2.0\dbhome set ORACLE_SID=ORCL set PATH=%ORACLE_HOME%\bin;%PATH%   cd %ORACLE_HOME%\OPatch datapatch -verbose     This forces Windows to use the 12.2 SQL*Plus first and the datapatch was successful.   2. Permanent Fix (system-wide) Go to System Properties → Environment Variables Edit the PATH variable Move D:\oracle\product\12.2.0\dbhome\bin above: D:\oracle\developer\BIN   Or remove the old Developer path completely if you no longer need it.  

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