Unable to login after "lock"

[Amila Liyanaarachchi]

When I lock the machine using Application menu > Lock or Right click
on the desktop > Lock screen it does not allow me to login back. Even
though I give the correct password it says "unlocking failed".
This only happens for the users that I created manually after the
installation, the user which I created during the installation does
not have this problem.
Any idea what has went wrong? Is there any additional permission
setting that I have to grant explicitly to the manually created users?