Another instance of OO is already running. OO won't open

When I try to open OpenOffice.org portable from my thumbdrive I get the message: "Another instance of OpenOffice.org is already running. Please close other instance of OpenOffice.org before launching OpenOffice.org for U3"

Well, I am in Chicago for the next three weeks and home is Arizona. I have also used it in California several weeks ago. How can I get this corrected?

I have removed OpenOffice portable from the thumbdrive and re-installed, but I get the same message.

[Moved to U3 Apps forum by moderator JTH. OpenOffice.org Portable is the open and free package that works from all drives, not just U3.]