locked applications can still be launched from terminal AFAIK, but you will have to type their name or directly execute their binaries . so if you happened to lock applocker , launch it from terminal then unblock it .
or unblock it manually by renaming it's .desktop file back to .desktop .
or apt-get reinstall applocker , that should also restore it's .desktop file .
if i am wrong on any of the above , some one plz correct me .