"Could not load file or assembly or one of its dependencies. An attempt was made to load a program with an incorrect format."

while debugging in VS, the error will be raised when starting debug in VS.

The error is below:

Could not load file or assembly 'p4dn, Version=1.0.1.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. An attempt was made to load a program with an incorrect 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.BadImageFormatException: Could not load file or assembly 'p4dn, Version=1.0.1.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. An attempt was made to load a program with an incorrect format.

Source Error: 

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.  

Stack Trace: 


[BadImageFormatException: Could not load file or assembly 'p4dn, Version=1.0.1.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. An attempt was made to load a program with an incorrect format.]
   System.Reflection.Assembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) +0
   System.Reflection.Assembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) +43
   System.Reflection.Assembly.InternalLoad(AssemblyName assemblyRef, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +127
   System.Reflection.Assembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +142
   System.Reflection.Assembly.Load(String assemblyString) +28
   System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +46

[ConfigurationErrorsException: Could not load file or assembly 'p4dn, Version=1.0.1.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. An attempt was made to load a program with an incorrect format.]
   System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +613
   System.Web.Configuration.CompilationSection.LoadAllAssembliesFromAppDomainBinDirectory() +203
   System.Web.Configuration.CompilationSection.LoadAssembly(AssemblyInfo ai) +105
   System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig) +178
   System.Web.Compilation.BuildProvidersCompiler..ctor(VirtualPath configPath, Boolean supportLocalization, String outputAssemblyName) +54
   System.Web.Compilation.ApplicationBuildProvider.GetGlobalAsaxBuildResult(Boolean isPrecompiledApp) +232
   System.Web.Compilation.BuildManager.CompileGlobalAsax() +51
   System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +337

[HttpException (0x80004005): Could not load file or assembly 'p4dn, Version=1.0.1.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. An attempt was made to load a program with an incorrect format.]
   System.Web.Compilation.BuildManager.ReportTopLevelCompilationException() +58
   System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +512
   System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters) +729

[HttpException (0x80004005): Could not load file or assembly 'p4dn, Version=1.0.1.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. An attempt was made to load a program with an incorrect format.]
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +8921851
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +85
   System.Web.HttpRuntime.ProcessRequestInternal(HttpWorkerRequest wr) +259

When i create a C# project which use 'p4dn.dll' there isn't this error coming across.

this is my first ASP project, i also read the similar questions like "http://stackoverflow.com/questions/41449/i-get-a-an-attempt-was-made-to-load-a-program-with-an-incorrect-format-error-o" and "http://stackoverflow.com/questions/1648213/could-not-load-file-or-assembly-xxx-or-one-of-its-dependencies-an-attempt-was". They cannot address my problem.

how can I solve this problem?

There is now a menu option to run the 64bit version of IIS Express. From Visual Studio menu select Tools -> Options... -> Projects and Solutions -> Web Projects

Click the button for "Use the 64 bit version of IIS Express for web sites and projects"