A few days ago a friend of mine had the Compiler Error Message: CS0433 error in his precompiled site, and proposed me a deal: a dinner for my help smile_regular , and since also Support Engineers sometimes need to eat, I accepted smile_wink .

The exact error message was the following: The type <typename> esists in both <path 1> and <path 2>. Sometimes the error message is quite self explanatory, especially if one of the two assemblies is in BIN and the other is in the GAC (remove the one in the BIN, you don't need two copies of the same file!), but my friend was getting the following one:

Exception information:
    Exception type: HttpCompileException
    Exception message: c:\WINNT\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\customers\30216428\89bd3cad\App_Web_default.aspx.27046288.rpug8fan.0.cs(112): error CS0433: The type 'App_Items_63_pgs_default' exists in both 'c:\WINNT\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\customers\30216428\89bd3cad\assembly\dl3\d1307a39\42cbc228_01a6c701\App_Web_tzn10d4k.DLL' and 'c:\WINNT\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\customers\30216428\89bd3cad\assembly\dl3\5493a6b9\8880bf21_01a6c701\App_Web_7jlq-fy_.DLL'

Thread information:
    Thread ID: 1
    Thread account name: <server>\ASPNET
    Is impersonating: False
    Stack trace:    at System.Web.Compilation.AssemblyBuilder.Compile()
   at System.Web.Compilation.BuildProvidersCompiler.PerformBuild()
   at System.Web.Compilation.BuildManager.CompileWebFile(VirtualPath virtualPath)
   at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile)
   at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile)
   at System.Web.Compilation.BuildManager.GetVirtualPathObjectFactory(VirtualPath virtualPath, HttpContext context, Boolean allowCrossApp, Boolean noAssert)
   at System.Web.Compilation.BuildManager.CreateInstanceFromVirtualPath(VirtualPath virtualPath, Type requiredBaseType, HttpContext context, Boolean allowCrossApp, Boolean noAssert)
   at System.Web.UI.PageHandlerFactory.GetHandlerHelper(HttpContext context, String requestType, VirtualPath virtualPath, String physicalPath)
   at System.Web.UI.PageHandlerFactory.System.Web.IHttpHandlerFactory2.GetHandler(HttpContext context, String requestType, VirtualPath virtualPath, String physicalPath)
   at System.Web.HttpApplication.MapHttpHandler(HttpContext context, String requestType, VirtualPath path, String pathTranslated, Boolean useAppConfig)
   at System.Web.HttpApplication.MapHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

As you can see, the two involved assemblies comes both from the Temporary ASP.NET Files folder and have randomly created names, so we needed some little more troubleshooting... I asked for the source code of the application and after flipping through a little bit, I notice he had a default.master page which he was using as the master for his default.aspx; interestingly both pages were implementing a class with the same name: public partial class App_Items_63_pgs_default.

That rang a bell... because what happens when you precompile the site is that you'll end up with two default.App_Item_63_pgs_default classes... I built a sample to confirm my theory:

   1: <%@ Master Language="C#" AutoEventWireup="true" CodeFile="default.master.cs" Inherits="_Default" %>   2: <html xmlns="http://www.w3.org/1999/xhtml">   3: <head runat="server">   4:     <title>Untitled Page</title>   5: </head>   6: <body>   7:     <form id="form1" runat="server">   8:         <asp:Label ID="Label1" runat="server" Text="Master"></asp:Label>   9:         <div>  10:             <asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">  11:             </asp:ContentPlaceHolder>  12:         </div>  13:         <asp:Label ID="Label2" runat="server" Text="Master"></asp:Label>  14:     </form>  15: </body>  16: </html>

   1: <%@ Page Language="C#" MasterPageFile="~/default.master" AutoEventWireup="true" CodeFile="Default.aspx.cs"    2:     Inherits="_Default" Title="Untitled Page" %>   3:     4: <asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" runat="Server">   5:     <asp:Label ID="Label3" runat="server" Text="Content"></asp:Label>   6: </asp:Content>

Publish the site and browse it, you should get the following error:

Server Error in '/TestPrecompiled' Application.

Compilation Error

Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately.

Compiler Error Message: CS0433: The type '_Default' exists in both 'c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\TestPrecompiled\b3047f60\f7364c3\assembly\dl3\6d1b8849\12db42f6_e9abc701\App_Web_yvefexa5.DLL' and 'c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\TestPrecompiled\b3047f60\f7364c3\assembly\dl3\a4f9584b\913c83f6_e9abc701\App_Web_qmnuz7n3.DLL'

Source Error:

Line 110:    
Line 111:    [System.Runtime.CompilerServices.CompilerGlobalScopeAttribute()]
Line 112:    public class default_aspx : global::_Default, System.Web.SessionState.IRequiresSessionState, System.Web.IHttpHandler {
Line 113:        
Line 114:        private static bool @__initialized;

Source File: c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\TestPrecompiled\b3047f60\f7364c3\App_Web_default.aspx.cdcab7d2.emhdmgwo.0.cs Line: 112

Bingo! We have a repro! smile_regular So I asked my friend to rename one of the two App_Item_63_pgs_default classes (or wrap them in two different namespaces) and the application magically started working fine.

I'm not completely clear why this happens only with the precompiled site while it works fine with the "normal" JITted site, but I'll try to find out.

It worth mentioning that you could get this compiler error if you upgrade your project to the Web Application Project you have with Visual Studio 2005 SP1 (or as a separate add-in); in that case pay attention to the @Page directive and change the CodeFile attribute to CodeBehind (further details in this post).

Again, when attempting to use the same CodeFile (.aspx.cs or .aspx.vb file) in Visual Studio 2005 for multiple ASPX or ASCX pages, compile errors resulted. Using a similar approach in Visual Studio .NET 2003 worked as desired. Visual Studio 2005 uses a “Partial Class” concept where declarations for “Controls” that are drag/dropped onto an ASPX page are put in a “.designer” file (which is typically stored in memory and not persisted to disk). The “designer” declarations are stored in the designer file and the actual C# or VB code is stored in the CodeFile. Because of the way that the ASPX/CodeFile/Designer go together, it isn’t straight forward to use multiple ASPX/Designer files with a single CodeFile since potentially unrelated controls from multiple ASPX pages will want to be declared in a single designer file. The recommended solution is to use the CodeFileBaseClass attribute of the ASPX page directive. When using this technique, each ASPX page has its own CodeFile/Designer files but then looks beyond these files for the base class that is specified.

Carlo

Quote of the Day:
Your heart often knows things before your mind does.
--Polly (Pearl) Adler