Include following code at the top of ascx page

<%@ Register TagPrefix="dnn" TagName="SOLPARTMENU" Src="~/Admin/Skins/SolPartMenu.ascx" %>

SkinObject	Code Snippet	Description	Example
dnn:SOLPARTMENU	< dnn:SolPartMenu runat="server" id="dnnSolPartMenu">	Displays the hierarchical navigation menu ( formerly [MENU] )