The SelectedValue property's value is not found in your listitem. Suppose you are getting selected value "10" but that is not present in your dropdownlist item. So you are getting exception. Whatever you are putting value as SelectedValue property that must be present in your dropdownlist Item.
Try code like below:
<asp:dropdownlist id="DropDownList1" runat="server" selectedvalue="<%# Bind("gender") %>" xmlns:asp="#unknown">
<asp:listitem text="gender" value="0"></asp:listitem>
<asp:listitem text="male" value="1"></asp:listitem>
<asp:listitem text="female" value="2"></asp:listitem>
</asp:dropdownlist>
Here I used value as 0,1,2 - you need to change what ever you are getting from "gender" column data.