Filter exception

[Dick]

I use a FilterTemplate (RadCombobox) in a RadGrid.

<EventOn:EventManagerGridTemplateColumn DataField="StatusType" UniqueName="StatusType" InterfaceMessageType="EventManagerGridHeaderStatusType" SortExpression="StatusType">
    <HeaderStyle Width="70px" />
    <FilterTemplate>
      <EventOn:EventManagerTypeFilterDropDown ID="ddStatusType" runat="server" EnumType="StatusType" CssClass="FormDropDown" Width="70px"
        DataValueField="StatusType" SelectedValue='<%# ((GridItem)Container).OwnerTableView.GetColumn("StatusType").CurrentFilterValue %>'
        OnClientSelectedIndexChanged="StatusTypeIndexChanged"/>

        <telerik:RadScriptBlock ID="RadScriptBlock1" runat="server">

            <script type="text/javascript">
                function StatusTypeIndexChanged(sender, args) {
                    var tableView = $find("<%# ((GridItem)Container).OwnerTableView.ClientID %>");
                    tableView.filter("StatusType", args.get_item().get_value(), "EqualTo");
                }
            </script>

        </telerik:RadScriptBlock>
    </FilterTemplate>
    <ItemStyle Width="50px" HorizontalAlign="Left" VerticalAlign="Top"></ItemStyle>
    <ItemTemplate>
         <EventOn:EventManagerTypeIcon ID="EventOnTypeIcon3" runat="server" Value='<%# Eval("StatusType")%>'></EventOn:EventManagerTypeIcon>
    </ItemTemplate>
</EventOn:EventManagerGridTemplateColumn>

I receive the following exception when filtering the column.

Runtime-fout Microsoft JScript: Sys.WebForms.PageRequestManagerServerErrorException: Neither of the types 'String' and 'StatusType' converts to the other

What am i doing wrong?