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'Failed to load file or assembly' System.Web.Helpers' or one of its dependencies

I get the following error when trying to start my ASP.NET project. Can anyone advise?

Could not load file or assembly 'System.Web.Helpers' or one of its dependencies. The located assembly manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040) 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.IO.FileLoadException: Could not load file or assembly 'System.Web.Helpers' or one of its dependencies. The located assembly manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040) 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. Assembly Load Trace: The following information can be helpful to determine why the assembly 'System.Web.Helpers' could not be loaded. === Pre-bind state information === LOG: DisplayName = System.Web.Helpers (Partial) WRN: Partial binding information was supplied for an assembly: WRN: Assembly Name: System.Web.Helpers | Domain ID: 2 WRN: A partial bind occurs when only part of the assembly display name is provided. WRN: This might result in the binder loading an incorrect assembly. WRN: It is recommended to provide a fully specified textual identity for the assembly, WRN: that consists of the simple name, version, culture, and public key token. WRN: See whitepaper http://go.microsoft.com/fwlink/?LinkId=109270 for more information and common solutions to this issue. LOG: Appbase = .../.../ LOG: Initial PrivatePath = \...\WebInterface\bin Calling assembly : (Unknown). === LOG: This bind starts in default load context. LOG: Using application configuration file: \...\WebInterface\web.config LOG: Using host configuration file: \Documents\IISExpress\config\aspnet.config LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v4.0.30319\config\machine.config. LOG: Policy not being applied to reference at this time (private, custom, partial, or location-based assembly bind). LOG: Attempting download of new URL /AppData/Local/Temp/Temporary ASP.NET Files/vs/0418a60d/21ffd41/System.Web.Helpers.DLL. LOG: Attempting download of new URL /AppData/Local/Temp/Temporary ASP.NET Files/vs/0418a60d/21ffd41/System.Web.Helpers/System.Web.Helpers.DLL. LOG: Attempting download of new URL .../.../bin/System.Web.Helpers.DLL. LOG: Using application configuration file: \...\WebInterface\web.config LOG: Using host configuration file: \Documents\IISExpress\config\aspnet.config LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v4.0.30319\config\machine.config. LOG: Redirect found in application configuration file: 2.0.0.0 redirected to 3.0.0.0. LOG: Post-policy reference: System.Web.Helpers, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35 LOG: Attempting download of new URL /AppData/Local/Temp/Temporary ASP.NET Files/vs/0418a60d/21ffd41/System.Web.Helpers.DLL. LOG: Attempting download of new URL /AppData/Local/Temp/Temporary ASP.NET Files/vs/0418a60d/21ffd41/System.Web.Helpers/System.Web.Helpers.DLL. LOG: Attempting download of new URL .../.../bin/System.Web.Helpers.DLL. WRN: Comparing the assembly name resulted in the mismatch: Major Version ERR: Failed to complete setup of assembly (hr = 0x80131040). Probing terminated. Stack Trace: [FileLoadException: Could not load file or assembly 'System.Web.Helpers' or one of its dependencies. The located assembly manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)] [FileLoadException: Could not load file or assembly 'System.Web.Helpers, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)] System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +0 System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +36 System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +152 System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean forIntrospection) +77 System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +21 System.Reflection.Assembly.Load(String assemblyString) +28 System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +38 [ConfigurationErrorsException: Could not load file or assembly 'System.Web.Helpers, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)] System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +738 System.Web.Configuration.CompilationSection.LoadAllAssembliesFromAppDomainBinDirectory() +217 System.Web.Configuration.CompilationSection.LoadAssembly(AssemblyInfo ai) +130 System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig) +170 System.Web.Compilation.BuildManager.GetPreStartInitMethodsFromReferencedAssemblies() +92 System.Web.Compilation.BuildManager.CallPreStartInitMethods(String preStartInitListPath, Boolean& isRefAssemblyLoaded) +290 System.Web.Compilation.BuildManager.ExecutePreAppStart() +157 System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException) +531 [HttpException (0x80004005): Could not load file or assembly 'System.Web.Helpers, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)] System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +9963380 System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +101 System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +254

I tried the following based on other answers:

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3 answers

The link to the version of the System.Web.Helpers assembly in the project may not match the version mentioned in the web.config file. Follow these steps.

  • Check out the reference version of System.Web.Helpers.
  • Check the web.config file under the root of the web application and see if there is an entry for System.Web.Helpers and check its version specified in the specified version.
  • Check the web.config file in the Views folder of the web application and see if there is an entry for System.Web.Helpers and check its version specified in the specified version.
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I had this problem. This was caused when I added the Razor view to the Web Forms project. Because of this action, Visual Studio added version 5 to .Net and made a number of other changes to the project.

I fixed the problem by going to Solution Explorer > Pending Changes . I noticed a whole bunch of unusual files. I right-clicked on any of the files and went to Source Control > Undo Pending Changes . I selected unusual files and Undo Changes , and after recovery it was fixed.

I saw how these additional files are added (for no apparent reason) at another time. Visual Studio does some luck-and-doodle thing for reasons not clear to me.

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I also had this problem when creating a new Razor view. The project was looking for a newer version of the dll System.Web.Helper and System.Web.WebPages. I solved this problem by editing my web.config and changing newVersion from 3.0.0.0 to 2.0.0.0. You can also completely remove them from web.config, like me.

  <dependentAssembly> <assemblyIdentity name="System.Web.Helpers" publicKeyToken="31bf3856ad364e35" /> <bindingRedirect oldVersion="1.0.0.0-3.0.0.0" newVersion="2.0.0.0" /> </dependentAssembly> <dependentAssembly> <assemblyIdentity name="System.Web.WebPages" publicKeyToken="31bf3856ad364e35" /> <bindingRedirect oldVersion="1.0.0.0-3.0.0.0" newVersion="2.0.0.0" /> </dependentAssembly>
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Source: https://habr.com/ru/post/1015694/

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