Can't edit a page because I'm already editing it on another computer??

Hi,

I recently upgraded to Contribute 4.0, but I encountered a problem today when I tried to update a page on our website.

I received an error message that I can't edit this page now because I'm editing it on another computer, which is impossible. No one else is logged in, so I don't know how this could be. I am able to make changes to other pages on the website, but not this one in particular.

Any idea what may be triggering this? Any help/guidance you can provide would be greatly appreciated! Keep it simple...I'm a beginner.

Thanks!