I am unable to use GVT in my application. The error is:

"Unknown server tag ''GVT:GridViewTree"

Here are the steps I have followed:

1. I have installed the GridViewTree.msi
2. Added "GridViewTree.dll" reference to the project.
3. Added this line to aspx page.
"<%@ Register Assembly="GridViewTree" Namespace="GridViewTree" TagPrefix="GVT" %>".
4. Added this code to aspx source.

<GVT:GridViewTree ID="GridViewTree1" runat="server" AllowSorting="True" AutoGenerateColumns="False" EnableViewState="False" FullPathDataColumn="FullPath"
IsParentDataColumn="IsFolder" OnRowCreated="GridViewTree1_RowCreated" ParentLevelStartSortByColumn="0">
<Columns>
<asp:BoundField DataField="FullPath" HeaderText="SalesPerson" SortExpression="FullPath">
<itemstyle wrap="True" />
</asp:BoundField>
<asp:BoundField DataField="CustomerID" HeaderText="Customer" SortExpression="CustomerID">
<itemstyle horizontalalign="Right" />
</asp:BoundField>
<asp:BoundField DataField="OrderDate" HeaderText="OrderDate" SortExpression="OrderDate">
<itemstyle horizontalalign="Right" />
</asp:BoundField>
<asp:BoundField DataField="UnitPrice" DataFormatString="{0:c}" HeaderText="UnitPrice"
SortExpression="UnitPrice">
<itemstyle horizontalalign="Right" />
</asp:BoundField>
<asp:BoundField DataField="Quantity" HeaderText="Quantity" SortExpression="Quantity">
<itemstyle horizontalalign="Right" />
</asp:BoundField>
<asp:BoundField DataField="Total" DataFormatString="{0:###,##0}" HeaderText="Total"
SortExpression="Total">
<itemstyle horizontalalign="Right" />
</asp:BoundField>
</Columns>
</GVT:GridViewTree>


Then it is throwing the error.

Is there anything that I should do to make it work?