After upgrading from 6.2.3 to 7.3.3 I received a similar error message when trying to view the Admin > Security Roles page. Sebastian's sql script fixed the problem. The Roles portion of the sql script applied specifically in my case.

Thanks Sebastian!! Keep up the great work!

     I met exactly the same issue today. When I click the DNN built-in menu "Admin - Security Roles", it throws the below error
    "Security Roles is currently unavailable. DotNetNuke.Services.Exceptions.ModuleLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DesktopModules.Admin.Security.Roles.FormatFrequency(String frequency) at ASP.desktopmodules_admin_security_roles_ascx.__DataBinding__control16"

    And I fixed this issue as follows:
    1. Open DesktopModules\Admin\Security\Roles.ascx.cs.
    2. Find
      protected string FormatFrequency(string frequency)
        {
            if (frequency == "N") return string.Empty;

            var ctlEntry = new ListController();
            ListEntryInfo entry = ctlEntry.GetListEntryInfo("Frequency", frequency);
            return entry.Text;
        }
    3. Change it as
       protected string FormatFrequency(string frequency)
        {
            if (frequency == "N") return string.Empty;

            var ctlEntry = new ListController();
            ListEntryInfo entry = ctlEntry.GetListEntryInfo("Frequency", frequency);
            return entry != null ? entry.Text : frequency;
        }

    4. As you can see, the error raise because entry is null in some cases.  So, we should check the null first,  then return related list entry.
        Wish above can help. If you don't know how to modify source code, mail me at xiaoqi98@msn.com, I will send my copy to you.
  
    

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