It seems that for some reason the permissions set control is missing from the pages permissions template. Or you are using template different than the default one. To be sure you are using the right one add the following attribute to the <cms>
node of the web.config
After that, check that the PagePermissions.ascx
file located under ~/Sitefinity/Admin/ControlTemplates
contains a PermissionsSet
control with this ID: PermissionSet1.
If this is not the case I have attached the default template which you should override with the previous one.
the Telerik team