You encounter that message when the unlocking is done on a folder that is mapped on the network. The folder that was supposedly locked is actually a network folder. You can't perform such operations on these folders unless the original PC is accessed through the desktop or remotely. Teamviewer might help you with this. Secondly, that message might appear when you're using the unlock feature on a shortcut. Try locating the original path of the locked folder and then use unlock again.
Unfortunately, this is the only support you can get about this software since it's discontinued.