How to fix error The method 'Skip' is only supported for sorted input in LINQ to Entities. The method 'OrderBy' must be called before the method 'Skip'.

In my case this error was a little misleading:
The method 'Skip' is only supported for sorted input in LINQ to Entities. The method 'OrderBy' must be called before the method 'Skip'.



to fix replace the following 
        <asp:GridView ID="GridView1" runat="server" ItemType="WebApplication9.Dpt" AutoGenerateColumns="False"
             AllowPaging="True" AllowSorting="True" PageSize="1" SelectMethod="GetDepartments">
            <Columns>
                <asp:BoundField DataField="DepartmentId" HeaderText="Department Id" SortExpression="DepartmentId" />
                <asp:BoundField DataField="DepartmentName" HeaderText="Department Name" SortExpression="DepartmentName" />
                <asp:TemplateField HeaderText="# of users in department">
                    <ItemTemplate><%#: Item.Users.Count() %></ItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>
with
        <asp:GridView ID="GridView1" runat="server" ItemType="WebApplication9.Dpt" AutoGenerateColumns="False" DataKeyNames="DepartmentId"
             AllowPaging="True" AllowSorting="True" PageSize="1" SelectMethod="GetDepartments">
            <Columns>
                <asp:BoundField DataField="DepartmentId" HeaderText="Department Id" SortExpression="DepartmentId" />
                <asp:BoundField DataField="DepartmentName" HeaderText="Department Name" SortExpression="DepartmentName" />
                <asp:TemplateField HeaderText="# of users in department">
                    <ItemTemplate><%#: Item.Users.Count() %></ItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>

I had gridview
        <asp:GridView ID="GridView1" runat="server" ItemType="WebApplication9.Dpt" AutoGenerateColumns="False"
             AllowPaging="True" AllowSorting="True" PageSize="1" SelectMethod="GetDepartments">
            <Columns>
                <asp:BoundField DataField="DepartmentId" HeaderText="Department Id" SortExpression="DepartmentId" />
                <asp:BoundField DataField="DepartmentName" HeaderText="Department Name" SortExpression="DepartmentName" />
                <asp:TemplateField HeaderText="# of users in department">
                    <ItemTemplate><%#: Item.Users.Count() %></ItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>
with selectMethod
        public IQueryable<Dpt> GetDepartments()
        {
            var query = this.db.Dpts
              .Include(c => c.Users);
            return query;
        }
and forgot data key names.....