转换nvarchar时，Asp QueryStringParameter转换失败

Question

当我运行以下代码时，我得到这个错误，全局s是静态int，我看了很多文章，但看不出这出错的地方：

  

异常详细信息：System.Data.SqlClient.SqlException：Conversion   将nvarchar值'glb.catID'转换为数据类型时失败   中间体

<asp:SqlDataSource ID="SqlDataSource1" runat="server" 
           ConnectionString="<%$ ConnectionStrings:CommerceConnectionString %>" 

           SelectCommand="select CategoryID, CategoryName, ProductImage,  Title,  SubCatID 
                          from Categories
                          JOIN Products
                          ON Categories.CategoryID= Products.CatID
                          WHERE CategoryID = @CategoryID AND SubCatID = @SubCatID ">
           <SelectParameters>
           <asp:QueryStringParameter Name="CategoryID"  QueryStringField="CategoryID" DefaultValue="glb.catID" /> 
           <asp:QueryStringParameter Name="SubCatID"  QueryStringField="SubCatID" DefaultValue="glb.subcatID"/>
           </SelectParameter