Server Error in '/' Application.

Input string was not in a correct format.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.FormatException: Input string was not in a correct format.

Source Error:

Line 42:         else if (Request.QueryString["nid"] != null)
Line 43:         {
Line 44:             int sid = Convert.ToInt32(Request.QueryString["nid"].ToString());
Line 45:             sql = "select * from [product] where classid=" + sid + "   ORDER BY [proxinhao] DESC";
Line 46:         }

Source File: d:\1\v8076983\wwwroot\Product.aspx.cs    Line: 44

Stack Trace:

[FormatException: Input string was not in a correct format.]
   System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal) +9593643
   System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info) +119
   System.Convert.ToInt32(String value) +48
   Product.DLNewsBind() in d:\1\v8076983\wwwroot\Product.aspx.cs:44
   Product.Page_Load(Object sender, EventArgs e) in d:\1\v8076983\wwwroot\Product.aspx.cs:18
   System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14
   System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35
   System.Web.UI.Control.OnLoad(EventArgs e) +91
   System.Web.UI.Control.LoadRecursive() +74
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2207

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.1040