Cannot drag column to group by

<telerik:RadGrid ID="gridLockbox" runat="server" PageSize="20" PagerStyle-PageButtonCount="5" AllowMultiRowSelection="true"
    OnNeedDataSource="gridLockbox_NeedDataSource" OnDetailTableDataBind="gridLockbox_DetailTableDataBind"
    OnItemDataBound="gridLockbox_ItemDataBound" OnUpdateCommand="gridLockbox_UpdateCommand"
    AllowPaging="true" AllowSorting="true" ShowGroupPanel="true" CellSpacing="0" Width="100%" Height="700px"
    RenderMode="Lightweight" ShowFooter="true" Skin="WebBlue">
    <GroupingSettings ShowUnGroupButton="True" CaseSensitive="false"/>
    <ClientSettings>
        <Scrolling AllowScroll="true" UseStaticHeaders="true" SaveScrollPosition="true" />
    </ClientSettings>
    <MasterTableView EditMode="PopUp" AutoGenerateColumns="false" AllowFilteringByColumn="true" DataKeyNames="TransUID"
        AllowMultiColumnSorting="true" CommandItemDisplay="None" TableLayout="Fixed" Font-Size="10">
        <DetailTables>
            <telerik:GridTableView DataKeyNames="RecordId" Name="Details" Width="100%" AutoGenerateColumns="false" TableLayout="Fixed">
                <Columns>
                    <telerik:GridBoundColumn DataField="FileOperation" HeaderText="File Operation" HeaderButtonType="None">
                        <HeaderStyle Width="180px" />
                    </telerik:GridBoundColumn>
                    <telerik:GridBoundColumn DataField="FileStatus" HeaderText="File Status" HeaderButtonType="TextButton">
                        <HeaderStyle Width="200px" />
                    </telerik:GridBoundColumn>
                    <telerik:GridDateTimeColumn DataField="CreatedDateTime" HeaderText="Created At">
                        <HeaderStyle Width="250px" />
                    </telerik:GridDateTimeColumn>
                    <telerik:GridBoundColumn DataField="Notes" HeaderText="Notes" HeaderButtonType="TextButton"></telerik:GridBoundColumn>
                </Columns>
            </telerik:GridTableView>
        </DetailTables>
        <GroupByExpressions>
            <telerik:GridGroupByExpression>
                <SelectFields>
                    <telerik:GridGroupByField FieldAlias="Date_Time" FieldName="Date_Time" FormatString="{0:MM/dd/yyyy}" HeaderValueSeparator=" from date: " />
                </SelectFields>
                <GroupByFields>
                    <telerik:GridGroupByField FieldName="Date_Time" SortOrder="Descending" />
                </GroupByFields>
            </telerik:GridGroupByExpression>
        </GroupByExpressions>
        <Columns>
            <telerik:GridEditCommandColumn UniqueName="EditColumn" HeaderText="Edit" Exportable="false">
                <HeaderStyle Width="50px" />
            </telerik:GridEditCommandColumn>
            <telerik:GridBoundColumn UniqueName="Lockbox" DataField="Lockbox" HeaderText="Lockbox" HeaderStyle-Width="180px" FilterControlWidth="70%">
                <FilterTemplate>
                    <telerik:RadComboBox RenderMode="Lightweight" ID="cmbLockbox" DataSource='<%#LockboxNames %>' DataTextField="Name"
                        DataValueField="ID" Width="150px" AppendDataBoundItems="true"
                        SelectedValue='<%# ((GridItem)Container).OwnerTableView.GetColumn("Lockbox").CurrentFilterValue %>'
                        runat="server" OnClientSelectedIndexChanged="LockboxIndexChanged">
                        <Items>
                            <telerik:RadComboBoxItem Text="All" />
                        </Items>
                    </telerik:RadComboBox>
                    <telerik:RadScriptBlock ID="RadScriptBlock1" runat="server">
                        <script type="text/javascript">
                            function LockboxIndexChanged(sender, args) {
                                var tableView = $find("<%# ((GridItem)Container).OwnerTableView.ClientID %>");
                                tableView.filter("Lockbox", args.get_item().get_value(), "EqualTo");
                            }
                        </script>
                    </telerik:RadScriptBlock>
                </FilterTemplate>
            </telerik:GridBoundColumn>
            <telerik:GridDateTimeColumn UniqueName="Date_Time" DataField="Date_Time" HeaderText="Date" DataFormatString="{0:MM/dd/yyyy}">
                <HeaderStyle Width="180px" />
            </telerik:GridDateTimeColumn>
            <telerik:GridBoundColumn UniqueName="TransSource" DataField="TransSource" HeaderText="Trans Type" Display="false"></telerik:GridBoundColumn>
            <telerik:GridNumericColumn UniqueName="Amount" DataField="Amount" HeaderText="Amount" DataType="System.Decimal" DataFormatString="{0:C}" FilterControlWidth="80%" Aggregate="Sum">
                <HeaderStyle Width="140px" />
            </telerik:GridNumericColumn>
            <telerik:GridBoundColumn UniqueName="ABA_RT" DataField="ABA_RT" HeaderText="Routing number">
                <HeaderStyle Width="200px" />
            </telerik:GridBoundColumn>
            <telerik:GridBoundColumn UniqueName="AccountNum" DataField="AccountNum" HeaderText="Account number">
                <HeaderStyle Width="210px" />
            </telerik:GridBoundColumn>
            <telerik:GridBoundColumn UniqueName="CheckNum" DataField="CheckNum" HeaderText="Check Number">
                <HeaderStyle Width="200px" />
            </telerik:GridBoundColumn>
            <telerik:GridBoundColumn UniqueName="FileOperation" DataField="FileOperation" HeaderText="File Operation">
                <HeaderStyle Width="200px" />
                <FilterTemplate>
                    <telerik:RadComboBox RenderMode="Lightweight" ID="cmbFileOperation" DataSource='<%#FileOperationNames %>' DataTextField="Name"
                        DataValueField="ID" Width="150px" AppendDataBoundItems="true"
                        SelectedValue='<%# ((GridItem)Container).OwnerTableView.GetColumn("FileOperation").CurrentFilterValue %>'
                        runat="server" OnClientSelectedIndexChanged="FileOperationIndexChanged">
                        <Items>
                            <telerik:RadComboBoxItem Text="All" />
                        </Items>
                    </telerik:RadComboBox>
                    <telerik:RadScriptBlock ID="RadScriptBlock2" runat="server">
                        <script type="text/javascript">
                            function FileOperationIndexChanged(sender, args) {
                                var tableView = $find("<%# ((GridItem)Container).OwnerTableView.ClientID %>");
                                tableView.filter("FileOperation", args.get_item().get_value(), "EqualTo");
                            }
                        </script>
                    </telerik:RadScriptBlock>
                </FilterTemplate>
            </telerik:GridBoundColumn>
            <telerik:GridBoundColumn UniqueName="FileStatus" DataField="FileStatus" HeaderText="FileStatus">
                <HeaderStyle Width="200px" />
                <FilterTemplate>
                    <telerik:RadComboBox RenderMode="Lightweight" ID="cmbFileStatus" DataSource='<%#FileStatusNames %>' DataTextField="Name"
                        DataValueField="ID" Width="150px" AppendDataBoundItems="true"
                        SelectedValue='<%# ((GridItem)Container).OwnerTableView.GetColumn("FileStatus").CurrentFilterValue %>'
                        runat="server" OnClientSelectedIndexChanged="FileStatusIndexChanged">
                        <Items>
                            <telerik:RadComboBoxItem Text="All" />
                        </Items>
                    </telerik:RadComboBox>
                    <telerik:RadScriptBlock ID="RadScriptBlock3" runat="server">
                        <script type="text/javascript">
                            function FileStatusIndexChanged(sender, args) {
                                var tableView = $find("<%# ((GridItem)Container).OwnerTableView.ClientID %>");
                                tableView.filter("FileStatus", args.get_item().get_value(), "EqualTo");
                            }
                        </script>
                    </telerik:RadScriptBlock>
                </FilterTemplate>
            </telerik:GridBoundColumn>
            <telerik:GridBoundColumn UniqueName="ImageFilePath" DataField="ImageFilePath" Display="false"></telerik:GridBoundColumn>
            <telerik:GridNumericColumn UniqueName="PaymentId" DataField="PaymentId" HeaderText="Payment Id" FilterControlWidth="70%">
                <HeaderStyle Width="120px" />
            </telerik:GridNumericColumn>
        </Columns>
        <EditFormSettings EditFormType="WebUserControl" UserControlName="LockboxCtrl.ascx">
            <PopUpSettings Modal="true" Width="1500px"/>
        </EditFormSettings>
    </MasterTableView>
</telerik:RadGrid>