OpenOffice.rog PE need to close all instances

This is my first time to install an OpenOffice.org or the Open Office applications Portable Edition. And I have no OpenOffice applications yet installed in my computer. I am just wondering why this error message showed up even if there is no existing open office application in my computer. How come that I have another instance of OpenOffice.org PE running in my task?

OpenOffice.org Portable | PortableApps.com Installer
Please close all instances of OpenOffice.org PE and then click Ok. The portable app cannot be upgraded while it is running.
