必须声明标量变量 - 删除命令

Question

当我运行此代码时，我得到代码，我得到错误必须声明标量变量。如果我只使用Vendor并删除删除参数，它可以正常工作，但仅适用于Vendor。删除过程正在使用自动生成列但删除按钮的GridView。我做错了什么？

<Columns>
    <asp:TemplateField>
        <ItemTemplate>
            <asp:LinkButton ID="DeleteBtn" runat="server" CommandName="Delete"
                OnClientClick="return isDelete();">Delete
            </asp:LinkButton>
        </ItemTemplate>
    </asp:TemplateField>
</Columns>

<asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ ConnectionStrings:TestAdamConnectionString %>" SelectCommand="SELECT * FROM [TestRedo]" OnSelecting="SqlDataSource2_Selecting"
    DeleteCommand="DELETE FROM [TestRedo] WHERE [Vendor] = @Vendor AND [Expiration] = @Expiration AND [ActionReq] = @ActionReq">
    <DeleteParameters>
        <asp:Parameter Name="Expiration" />
        <asp:Parameter Name="ActionReq"/>
    </DeleteParameters>
</asp:SqlDataSource>