I am having this same problem. Contribute CS3 v4.1

Before I check out the file, there is no lock. When I click checkout, it
creates a lock and then tells me "you can't edit this page now because you are
already editing it on another computer. Click here to make this page editable."
When I click on that, I get a dialog box asking if I'm sure I want to remove
the lock. If I say "Yes", it removes the lock, and the page is no longer
editable. I am back to square 1.

If I delete the lock, it just makes a new one when I click on edit this page.

I can edit / checkout via Dreamweaver just fine. This seems to be a Contribute
deal. It's almost like it's making the lock first, then trying to get the file,
but whoa-- it's locked.