No assembly found containing an OwinStartupAttribute Error

Question

This error   The following errors occurred while attempting to load the app  - No assembly found containing an OwinStartupAttribute  - The given type or method  false  was not found  Try specifying the Assembly  To disable OWIN startup discovery  add the appSetting owin AutomaticAppStartup with a value of  false  in your web config  To specify the OWIN startup Assembly  Class  or Method  add the appSetting owin AppStartup with the fully qualified startup class or configuration method name in your web config   appears on my screen on the most face burningly ugly error page ever created in history      Ive tried to follow the instructions on the page by inserting the owin AutomaticAppStartup in the config     lt appSettings  gt       lt add key  owin AppStartup  value  false  gt  lt  add gt           lt  appSettings gt    this did not fix the problem  Any suggestions

User · Answer

Add the following key in Web config will remove the code   lt appSettings gt      lt add key  owin AutomaticAppStartup  value  false    gt    lt  appSettings gt

User · Answer

just replacing           using  WebApp Start url     with           using  WebApp Start lt Startup gt  url     solved my problem  The class named Startup was already implemented  as mentioned above by  robthedev

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I know this post is old but just in case someone is looking for the same error  try adding   lt add key  owin AutomaticAppStartup  value  false  gt  lt  add gt    after the tag  lt appSettings gt   and if afterwards the next error show up       HTTP Error 401 0 - Unauthorized error message   add the next code after the tag  lt system web gt  it can be at the beginning    lt authentication mode  Forms  gt         lt forms loginUrl    YourFolderName yourFileName  timeout  1    gt       lt  authentication gt   In my case is    lt authentication mode  Forms  gt         lt forms loginUrl    Login Index  timeout  1    gt       lt  authentication gt

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just paste this code   lt add key  owin AutomaticAppStartup  value  false    gt   in Web config Not In web config  there is two webconfig so be sure that it will been paste in Web Config

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Check if you have the Startup class created in your project  This is an example   using Microsoft Owin  using Owin    assembly  OwinStartupAttribute typeof  project name  Startup     namespace AuctionPortal       public partial class Startup               public void Configuration IAppBuilder app                        ConfigureAuth app

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I deleted all DLLs from the branch which wasn t working  then I copied all DDls from my branch which was working to my branch wich wasn t  This solved the issue

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Add below code to your web config file then run the project          lt runtime gt       lt assemblyBinding xmlns  urn schemas-microsoft-com asm v1  gt       lt dependentAssembly gt       lt assemblyIdentity name  Microsoft Owin Security  publicKeyToken  31bf3856ad364e35   gt       lt bindingRedirect oldVersion  1 0 0 0-3 0 1 0  newVersion  3 0 1 0   gt       lt  dependentAssembly gt       lt dependentAssembly gt       lt assemblyIdentity name  Microsoft Owin Security OAuth  publicKeyToken  31bf3856ad364e35   gt       lt bindingRedirect oldVersion  1 0 0 0-3 0 1 0  newVersion  3 0 1 0   gt       lt  dependentAssembly gt       lt dependentAssembly gt       lt assemblyIdentity name  Microsoft Owin Security Cookies  publicKeyToken  31bf3856ad364e35   gt       lt bindingRedirect oldVersion  1 0 0 0-3 0 1 0  newVersion  3 0 1 0   gt       lt  dependentAssembly gt       lt dependentAssembly gt       lt assemblyIdentity name  Microsoft Owin  publicKeyToken  31bf3856ad364e35   gt       lt bindingRedirect oldVersion  1 0 0 0-3 0 1 0  newVersion  3 0 1 0   gt       lt  dependentAssembly gt       lt  runtime gt

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you may not have Configuration method in the class you mentioned in   lt appSettings gt   lt add key  owin AppStartup  value  WebApplication1 App Start Startup   gt

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I was missing the attribute    assembly  OwinStartupAttribute typeof projectname Startup      Which specifies the startup class  More details  https   docs microsoft com en-us aspnet aspnet overview owin-and-katana owin-startup-class-detection

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Add class Startup cs to root of project with next code   using Microsoft Owin  using Owin    assembly  OwinStartupAttribute typeof ProjectName Startup    namespace ProjectName       public partial class Startup               public void Configuration IAppBuilder app                        ConfigureAuth app

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Check you have the correct startup project selected  I had a web api project as startup  That generated this error

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If deploying to Azure and you get this error  Simply delete all files on the site  backup any web config  appsettings json or whatver you do not want to loose  and deploy again  There are some left over dll files that should not be on the site  that makes the Azure portal think it needs to use OWIN

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I wanted to get rid of OWIN in the project    Delete OWIN references and Nuget packages from project Clean  amp  Rebuild project Run app   Then I got OWIN error  These steps didn t work  because OWIN dll was still in bin  directory   FIX    Delete bin  directory manually Rebuild project

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For those who do want owin to start   lt add key  owin AutomaticAppStartup  value  false    gt  won t work  but the following worked for me    if you have a partial class  Startup  in your Startup Auth file  create another partial Startup class in the root of your project  define an assembly owinstartup attribute pointing to that class create a  Configuration  method rebuild your application   You could also create the  Configuration  method  and add the assembly attribute to the Startup Auth  but doing it this way allows you to keep your Startup class separated by leveraging C  class definition splitting  Read more here  https   docs microsoft com en-us dotnet csharp programming-guide classes-and-structs partial-classes-and-methods  This is what my Startup cs file looked like   using Microsoft Owin  using Owin    assembly  OwinStartupAttribute typeof ProjectNameSpace Startup     namespace ProjectNameSpace       public partial class Startup               public void Configuration IAppBuilder app                        ConfigureAuth app

User · Answer

if you want to use signalr  you haveto add startup cs Class in your project  Right Click In You Project Then Add New Item And Select OWIN Startup Class  then inside Configuration Method Add Code Below  app MapSignalR      I Hope it will be useful for you

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I got this error because there was an extra white space in the code  Instead of    lt add key  owin AutomaticAppStartup  value  false    gt   It was   lt add key  owin AutomaticAppStartup   value  false    gt

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Add this code in web config under the  lt configuration gt  tag as shown in image below  Your error should then be gone    lt configuration gt     lt appSettings gt       lt add key  owin AutomaticAppStartup  value  false    gt     lt  appSettings gt         lt  configuration gt

[c#] No assembly found containing an OwinStartupAttribute Error

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