SharePoint 2007 - The file xyz is checked out or locked for editing by someone else

I ran into this annoying error today, when trying to check in a word 2007 document into a SharePoint document library with versioning enabled:

"The file xyz is checked out or locked for editing by someone else"

I was logged into the sharepoint site as the correct user, and I had opened the file in word 2007 and authenticated again as the same user, and I still get that message.

To fix the problem, I had to disable the web client service on my local machine as shown in the screenshot below. Once I did that, closed word 2007, then made my changes again and tried to do a checkin, everything worked as it should.

Another thing to note is that this site was in my trusted zone, not my local intranet zone, and the sharepoint server is on a different domain than the one my workstation is logged into. I'm not sure if those are factors at this point.