Hi,
User does not have needed capability. Use “Admin menu add-on” to know, what it is.
If you wish to see full list of administrator menu items open “Admin menu” for the “Administrator” role.
There is no sense to block menu items for administrator. So checkboxes are unavailable here. It is a very good start point for WordPress menu user permissions study and research. You may use “Admin Menu” dialog here as the reference for your work with roles and capabilities as “Admin Menu” shows what user capability restricts access to what admin menu item including menu items added by active plugins.
Some plugins use own user capabilities, some plugins use one from WordPress built-in capabilities, like ‘manage_options’, ‘edit_posts’, etc.
The 1st step is to look what capabilities plugin uses to protect its menu. Open “Admin menu” for the ‘Administrator’ role, find needed menu item and look to the ‘User Capability’ column.