Certain Users haven't been granted permission to unlock Cases based on their assigned Security Profile, they will need to raise the issue with an Administrator.
Alternatively, if a User does have unlock rights, but cannot unlock a Case, the User may be in the 'My Cases' or 'My Home' view in versaSRS and they need to access the Team that the Case is logged in and try again.
If there are still unlock issues a Case needs to be raised with VersaDev Support, please include all findings from above.