Databinding expressions are only supported on objects that have a DataBinding event

I have this function that checks the current status of checkbox. It
works great on almost all my controls. I use to determine if I will
make certain textboxes and labels visible.

However, when I attempt to use it to disable certain items in a
dropdownlist, I get this error:

Parser Error Message: Databinding expressions are only supported on
objects that have a DataBinding event.
System.Web.UI.WebControls.ListItem does not have a DataBinding event.


I'm trying to use it as follows:

<asp:ListItem Selected="True" Value="">None</asp:ListItem>
<asp:ListItem Value="RT-BUYNOW"
>BUY NOW $3.50 MORE MINUTES</asp:ListItem>
<asp:ListItem Value="RT-RECHARGE" Enabled='<%# CashorCredit()%>'>$20
OFF NEXT RECHARGE</asp:ListItem>
</aspropDownList><br />




It's works when I use here:

<asp:TextBox ID="cityTextBox" maxlength="20" Visible='<%#
CashorCredit()%>' runat="server" SkinID="Retailer"
Text='<%# Bind("city") %>' Width="149px" />
<br>

Thanks for any help or information.