During recent PSU apply I faced this issue, I was to patch Patch 11724977 - 10.2.0.4.8 Patch Set Update and for it pre requisite is 9352164 - 10.2.0.4.4 Patch Set Update. Though it is clearly documented that OPatch should be 10.2.0.5 or later due to negligence triggered the below command to check the conflict. after few minutes search found some clue and checked the Opatch version.

So thought to share how to overcome by new opatch. 

>opatch prereq CheckConflictAgainstOHWithDetail -phBaseDir ./9352164
Invoking OPatch 10.2.0.4.2

Oracle Interim Patch Installer version 10.2.0.4.2
Copyright (c) 2007, Oracle Corporation.  All rights reserved.

PREREQ session

Oracle Home       : /u001/app/oracle/product/10.2.0
Central Inventory : /u001/app/oracle/oraInventory
   from           : /etc/oraInst.loc
OPatch version    : 10.2.0.4.2
OUI version       : 10.2.0.4.0
OUI location      : /u001/app/oracle/product/10.2.0/oui
Log file location : /u001/app/oracle/product/10.2.0/cfgtoollogs/opatch/opatch2012-07-21_21-58-10PM.log

Invoking prereq "checkconflictagainstohwithdetail"
The location "./9352164/README.html" is not a directory or a valid patch zip file.
Prereq "checkConflictAgainstOHWithDetail" not executed
PrereqSession failed: Invalid patch location.

OPatch failed with error code 73

download appropriate Opatch from metalink and unzip
> unzip p6880880_102000_LINUX.zip
you will get a directory named OPatch

cd $ORACLE_HOME
mv OPatch OPatch_old

cd to_the_directory_where_you_unzipped_above_patch

mv OPatch $ORACLE_HOME

Now check the opatch version.
export PATH=$PATH:$ORACLE_HOME/OPatch

> opatch version
Invoking OPatch 10.2.0.5.1

OPatch Version: 10.2.0.5.1

OPatch succeeded.

>opatch prereq CheckConflictAgainstOHWithDetail -phBaseDir ./9352164
Invoking OPatch 10.2.0.5.1

Oracle Interim Patch Installer version 10.2.0.5.1
Copyright (c) 2010, Oracle Corporation.  All rights reserved.

PREREQ session

Oracle Home       : /u001/app/oracle/product/10.2.0
Central Inventory : /u001/app/oracle/oraInventory
   from           : /etc/oraInst.loc
OPatch version    : 10.2.0.5.1
OUI version       : 10.2.0.4.0
OUI location      : /u001/app/oracle/product/10.2.0/oui
Log file location : /u001/app/oracle/product/10.2.0/cfgtoollogs/opatch/opatch2012-07-21_23-01-46PM.log

Patch history file: /u001/app/oracle/product/10.2.0/cfgtoollogs/opatch/opatch_history.txt

Invoking prereq "checkconflictagainstohwithdetail"

Prereq "checkConflictAgainstOHWithDetail" passed.

OPatch succeeded.