Communication is sometimes difficult.  I don't know why you'd use MENU instead of SOLPARTMENU, or several other things you have there like the odd names.  Here is some working .ascx code from one of my vertical menu skins, look at it and use it as a starting point if you can:

At the top of the page:
<%@ Register TagPrefix="dnn" TagName="SOLPARTMENU" Src="~/Admin/Skins/SolPartMenu.ascx" %>

And for placement of the menu:
<dnn:SOLPARTMENU runat="server" id="dnnSOLPARTMENU" separatecss="true" fontnames="Arial" fontsize="10" Display="Vertical" UseRootBreadcrumbArrow="False" UseSubMenuBreadcrumbArrow="True" UseArrows="True" rootmenuitembreadcrumbcssclass="MainMenu_MenuItemSel"  />

Best regards,

PS, following is the setting of css:.

MainMenu_MenuContainer
{
    width: 175px;
    background-color: #993300;
  
  
}
.MainMenu_MenuBar
{
    cursor: pointer;
    cursor: hand;
    height: 25px;
    background-color: transparent;
    padding-left: 20px;
}
.MainMenu_MenuItem
{
    border-left: #ffd085 0px solid;
    border-bottom: #993300 1px solid;
    border-top: #993300 1px solid;
    border-right: #ffd085 0px solid;
    cursor: pointer;
    cursor: hand;
    color: white;
    font-family: PMingLiU, Tahoma, Arial, Helvetica;
    font-size: 10pt;
    font-weight: normal;
    font-style: normal;   
    background-color: transparent;
    background-image: url(dot.gif);
    background-repeat: repeat-x;
    background-position-y: bottom;
}
.MainMenu_MenuIcon
{
    background-color: #cc3300;
    border-left: #cc3300 1px solid;
    border-bottom: #cc3300 1px solid;
    border-top: #cc3300 1px solid;
    cursor: pointer;
    cursor: hand;
    text-align: center;
    width: 15px;
    height: 21px;
  
}
.MainMenu_SubMenu
{
    background-color: #993300;
    z-index: 1000;
    cursor: pointer;
    cursor: hand;
    filter: progid:DXImageTransform.Microsoft.Shadow(color=      '#696969' , Direction=135, Strength=3);
    border: 2px;
}

.MainMenu_MenuBreak
{
    height: 10px;
    background-color: transparent;
}
.MainMenu_MenuItemSel
{
    background-color: goldenrod;
    cursor: pointer;
    cursor: hand;
    color: #000000;
    font-family: PMingLiU, Tahoma, Arial, Helvetica;
    font-size: 10pt;
    font-weight: normal;
    font-style: normal;
    background-image: url(dot.gif);
    background-repeat: repeat-x;
    background-position-y: bottom;
}
.MainMenu_MenuArrow
{
    border-right: #993300 1px solid;
    border-bottom: #993300 1px solid;
    border-top: #ffd085 0px solid;
    font-family: webdings;
    font-size: 10pt;
    cursor: pointer;
    cursor: hand;
}
.MainMenu_RootMenuArrow {
 font-family: webdings;
 font-size: 10pt;
 cursor: pointer;
 cursor: hand;