MunyaM Having an agent set as admin just gives them access to the Admin panel, it doesn't actually affect ticket permissions at all (although with admin access an agent could set their own permissions to whatever they wanted!).

Permission to close tickets is defined via roles - for the affected agent(s) check the role in Admin -> Agents -> Agents -> [agent name] -> Access ensuring you verify the role for the relevant department.

The permissions for each role can be verified in Admin -> Agents -> Roles. Here, ensure the role assigned to each department has the close tickets permission.

Admin privs have nothing to do with what they can and cannot access and do.

Go to their Account and see their Role.
Admin panel -> Agents -> Agents
Click on their account.
Click on the Access tab, and note their assigned Role.

Now go to
Admin panel -> Agents -> Roles
Click their Role that you noted.
Click on the Permissions Tab.
Ensure that their Role grants them Close.