Getting a 'page not found' error when clicking publish

Hi, I am getting the following error (screenshot attached) when saving or publishing posts in wordpress. This happens sometimes, not 100% of the time.

https://dl.dropbox.com/u/8413898/Screen%20shot%202011-08-18%20at%208.57.50%20AM.png

My wordpress installation is up to date, and I’ve upgraded the wordpress database. Can anyone provide any insight on this error?

Thanks!

https://plpnetwork.com