Get rid of %COMSPEC% and the Nul stuff as it does nothing for you.

If the uninstaller supports silent switches it will be silent.

Code:
Shell 'C:\WINDOWS\uninst.exe -y -f"C:\Program Files\Pivotal\Relation\DeIsL1.isu"


Though I can pretty much tell you that it isn't going to work that way.

Just sit there at the command line in a DOS prompt and type in those commands to see if you can get it to uninstall silently or not.

uninst.exe -y -f"C:\Program Files\Pivotal\Relation\DeIsL1.isu
uninst.exe -s -f"C:\Program Files\Pivotal\Relation\DeIsL1.isu
uninst.exe /y -f"C:\Program Files\Pivotal\Relation\DeIsL1.isu
uninst.exe /s -f"C:\Program Files\Pivotal\Relation\DeIsL1.isu

etc... if you can't find a combination that works then KiX can't do it either.

This software, can it be mailed or downloaded and installed as a test? I'm sure it can be removed by brute force as well but one needs to know what all it installs and where first.

.