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16-bit applications behave strangely after installation of ClearCase



This technote explains why 16-bit applications behave strangely after installation of IBM® Rational® ClearCase® along with the steps on how to resolve the problem.


After installing ClearCase, strange interactions occur when running some 16-bit applications such as "EDIT" or "COMMAND.COM" outside or inside of Rational ClearCase.

Note: If ClearCase is uninstalled, the problem goes away.

If the ClearCase installation was configured to support 16 bit auditing, ClearCase installs ccasevdd.dll (a virtual device driver) and adds the following registry key:


whose value is the path to ccasevdd.dll.

Anytime a true 16-bit application is run, Windows® runs the above ccasevdd.dll device driver. This has been known to cause some interactions with the 16 bit tools or applications.

Resolving The Problem

Note: The following directions require you to edit the registry using the Windows Registry Editor. However, editing the Windows Registry incorrectly can cause serious problems that may require you to reinstall your operating system. Use Registry Editor at your own risk. Before proceeding review the Microsoft article, 256986 - Description of the Microsoft Windows Registry.

To correct this problem, remove the path value in the above key (path to ccasevdd.dll), but do not remove the key itself since other applications may need to install their own virtual device driver in the future.

Restart the machine. The 16-bit application or tool will now behave normally.

Note: If you are running a tool under an Omake environment or plan to use Omake and require auditing of 16-bit tools, use vdmaudit as detailed in the Omake manual.


Hardcopy can be ordered from the IBM Publications Center

On-line documentation can be found:

  • HTML

  • Distributed Documentation
    Windows®: C:\Program Files\Rational\ClearCase\doc\books

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    Document Information

    Modified date:
    16 June 2018