UtilSession failed: Prerequisite check "CheckActiveFilesAndExecutables" failed

Problem Description
When applying a Opatch to a 10.2.0.x installation, applying OPatch failed with the following error:

Running prerequisite checks...
Prerequisite check "CheckActiveFilesAndExecutables" failed.
The details are:

Following executables are active :
/u01/app/oracle/product/10.2.0/lib/libnmemso.so
UtilSession failed: Prerequisite check "CheckActiveFilesAndExecutables" failed.

OPatch failed with error code 73

Cause of the Problem
The problem happened because a process is still using the libnmemso.so library which violates prerequisite check of installing one-off patches or patchsets. To install Opatch or patchsets all processes that use the $ORACLE_HOME being patched MUST be shutdown cleanly, this would include databases, listeners, intelligent agents, database control etc.

Solution of the Problem
A similar type of error and solution is discussed in http://arjudba.blogspot.com/2010/03/opatch-failed-with-error-code-74.html.

To implement the solution, please execute the following steps:

Step 01: Identify the process that is using the library libnmemso.so

$ fuser /u01/app/oracle/product/10.2.0/lib/libnmemso.so

Step 02: Stop that process. libnmemso.so library is used by EM and so often it is necessary to stop the enterprise manager control process.

$ emctl stop

Step 03: After it is stopped apply the patch

Step 04: Restart any processes that were previously stopped.

Related Documents
OPatch failed with error code 74 - CheckActiveFilesAndExecutables failed
How to Download Patchset or Opatch from metalink
List of Patchset number in metalink