Disable multiple selection
You can prevent users from applying actions to multiple items in a
      single right-click. In the accessrights.dtd file, you add
      the multiselect-disabled attribute to the file and then set
      the multiselect-disabled attribute to true for each menu option that you want to disable. 
When this attribute is set for a menu option, if a user selects multiple
            items and right-clicks to open the menu, the menu option is disabled. If you  also set
            the hide-when-disabled attribute to true, it is also hidden.
Important: Make configuration changes in a test
            environment and confirm they work before copying them to a production
            environment.
         Note: Configuring this setting
            overrides any default behavior.
        To disable multiple selection: