FormView Control And Javascript Popup Calendar?

Hello: i have javascript code for a popup calendar and works fine if a form is a form control:
<form id="FormView1" runat="server">

however, if i use my formview control w/ the same code for a formview control, it doesn't put the value back into my text box txtDate after the user selects the date:

<asp:FormView ID="FormView1" runat="server">
<asp:TextBox ID="txtDate" runat="server" TabIndex="3" Width="65px" ></asp:TextBox>
<a onmouseover="window.status ='Please Select Date';return true;"
onmouseout="window.status='';return true;"
href="javascript:show_calendar('FormView1.txtDate');">
<img alt="open calendar" src="images/SmallCalendar.gif"/></a>

this seems to be the only difference so i was wondering if perhaps i need to reference this form in a different way? i don't know why it won't work for my formview control.