Is this happens with all the pages or just for a particular page?
Please navigate (FTP) to the server and check any lock file (.LCK) has been aleady present. If so delete it the lock file and try editing again.
Hope this helps you.
This happens to all the pages. If I go and remove the .LCK file, then it works, but then the same problem happens again.
Can you please let me know the content of the lock file? It should have username and email adress of the person placed the page in edit mode.
Since I don't have an actively locked file right now, I'll have to ask my client to go in and edit a page (and get the error again), so that I can send the .lck file to you. Thanks for helping me with this.