The type or namespace IAppBuilder could not be found(missing using a directive pr an assembly reference)

I am working on an Asp.Net MVC 4 Application in which I am using SignalR 2.0.1 and I Mapped it using Owin Startup class and it worked fine at first.

All of a sudden when I tried to rebuild my app it said that the type are namespace IAppbuilder could not be found.

Following is my start up class

using Microsoft.Owin;
using Owin;
using WhiteBoardApp;

namespace WhiteBoardApp
{
    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            app.MapSignalR();
        }
    }
}

I have installed Owin package too, and for some reasons I could not find Owin Startup class so I just added a normal class and included all the references that are needed. May I know where I am making a mistake

Try to use Package Manage Console and do

Update-Package Owin -Reinstall

I was having similar issue. But instead Owin, problem was causing Microsoft.Owin, obviously

Update-Package Owin -Reinstall

Didn't work, neither did Update-Package Owin

BUT

Install-Package Microsoft.Owin

did work fine for me, thanks.

The IAppBuilder interface is found under Owin package. Just add a reference in your class file:

using Owin;

And rebuild. Your project will pick this up.

I have no idea why VS didn't pick this up, but it didn't. Once I added this reference to my project, then everything fell into place.

I encountered the same problem while building my project. Here are the steps that helped fix my problem:

1. Go to Solution Explorer and look for your project
2. Under your project, expand the References; You should see warnings on the problematic reference
3. Right click References and open Manage NuGet Packages
4. Search the name of problematic reference i.e. Microsoft.Owin; After loading it shows that it is already installed (It is, but it installed incorrectly. Checking the properties > version at step 2 shows 0.0.0.0)
5. Check Force uninstall, even if there are dependencies on it
6. Uninstall
7. Install
8. Build and run the project

Problems

Cannot install Microsoft.Web.Infrastructure because it already exists in the packages folder. Rolling back...

1. Go to your project folder and look for packages
2. Find the problematic package i.e. Microsoft.Web.Infrastructure
3. Delete the folder
4. Resume from step 7

Alternatives

Here are the alternatives I've read about to fix this kind of problem.

• Clean and Rebuild Project / Solution
• Restart Visual Studio
• Restart PC

Good luck.