Contribute 3: can't unlock the edited page sent to a reviewer

In Contribute 3, you have the possibility to send an edited page to another person for review. Until this review is finished, this page is locked and cannot be downloaded for re-editing. In my case, the reviewer has somehow deleted this page and downloading for re-editing remains locked. According to the Contribute 3 Manual, in order to un-lock, you ad the ending “.lck” to the filename, e.g. www.xyz.index.html.lck. By doing so, you may delete this page and un-lock. However, when I try it, I get the message that either the file does not exist anymore or that I do not have the role of an administrator. I then made sure that I am administrator and yet, I still cannot unlock that page. For this case, the Contribute 3 Help gives no further advice. Therefore, I would appreciate if anyone would know a way around this problem. Many thanks in advance