0
take the dropdown values as follows
<asp:DropDownList ID="DropDownList1" runat="server">
<asp:ListItem>select Color</asp:ListItem>
<asp:ListItem>Red</asp:ListItem>
<asp:ListItem>green</asp:ListItem>
<asp:ListItem>bluee</asp:ListItem>
</asp:DropDownList>
<asp:CheckBoxList ID="CheckBoxList1" runat="server">
<asp:ListItem>Red</asp:ListItem>
<asp:ListItem>green</asp:ListItem>
<asp:ListItem>bluee</asp:ListItem>
</asp:CheckBoxList>
and write the following code in buton click event
if (DropDownList1.SelectedIndex!= 0)
{
CheckBoxList1.SelectedIndex = DropDownList1.SelectedIndex-1;
}
all the best
M.KoteswaraRao.