selling my laptop. can't "remove device" from ubuntuone

I'm selling my laptop, with Ubuntu 11.04 installed. I don't want to leave any security holes on this machine.

I've set up TomBoy notes to synch to Ubuntu One. Tomboy won't let me change the synchronization settings
(remove access to my Ubuntu One)

I can't get Ubuntu One to "remove device". When I log in and click the remove button next to the device name,
I am immediately logged out of Ubuntu One, no warning, no explanation, NO REMOVAL. The next time I log in,
the device I want to remove is STILL THERE. In fact, it's listed twice!

I've tried this via System>Preference>Ubuntu One AND using my Firefox browser, at page

https://one.ubuntu.com/

I can't find any tutorial or how-to that specifically outlines this procedure. They all say "devices can be removed"
but don't explain HOW

Now if you are kind enough to reply, please DON'T ASSUME I know ANYTHING. Explain the entire process IN DETAIL.

I can't sell this laptop until this task is accomplished!

Thanks