Problem with OPatch

Today I hit a problem with installation of a patchset. Details below:

[oracle@yyy]$ opatch prereq CheckConflictAgainstOHWithDetail -phBaseDir ./19121548
Oracle Interim Patch Installer version 11.2.0.3.5
Copyright (c) 2013, Oracle Corporation.  All rights reserved.

PREREQ session

Oracle Home       : /oracle/product/11.2.0.3
Central Inventory : /oracle/oraInventory
   from           : /oracle/product/11.2.0.3/oraInst.loc
OPatch version    : 11.2.0.3.5
OUI version       : 11.2.0.3.0
Log file location : /oracle/product/11.2.0.3/cfgtoollogs/opatch/opatch2014-08-08_13-19-37PM_1.log

Invoking prereq "checkconflictagainstohwithdetail"
List of Homes on this system:

  Home name= OraDb10g_home1, Location= "/oracle/product/102"
  Home name= OraDb11g_home1, Location= "/oracle/product/11.2.0.2"
  Home name= agent10g1, Location= "/oracle/oagent/product/10.2.0/agent10g"
Prereq "checkConflictAgainstOHWithDetail"not executed 
Unable to create Patch Object.
Exception occured : null

OPatch succeeded.

Colleagues of mine suggested to rebuild the Oracle inventory.

[oracle@yyy bin]$ ./runInstaller -silent -invPtrLoc $ORACLE_HOME/oraInst.loc -attachHome ORACLE_HOME="/oracle/product/11.2.0.3" ORACLE_HOME_NAME="Ora11gR2home"
Starting Oracle Universal Installer...

Checking swap space: must be greater than 500 MB.   Actual 1239 MB    Passed
'AttachHome' failed.
'AttachHome' failed.

The solution is quite simple. First one have to remove any remnants of current Oracle inventory. Then the inventory operation starts to work properly. With the inventory rebuild the OPatch also starts to work properly.