SignalR no longer working "No assembly found containing an OwinStartupAttribute"
Solution 1
I had this error during Identity Framework 2.0 integration. Adding Following in Web.config file of the project solved it:
<appSettings>
<add key="owin:AutomaticAppStartup" value="false" />
</appSettings>
Solution 2
It seems that Nuget didn't upgrade the SignalR dependencies properly (it must check that the version is in range and not bother updating) so 2 versions of the OWIN assemblies were being used in the solution.
So in the WebApi Project : SignalR 2.1.0 and Microsoft.Owin 2.0.2.0
and in another project : SignalR 2.1.0 and Microsoft.Owin 2.0.1.0
Visual Studio doesn't pick up the version incompatibilities on build either, so when the Web project loads up OWIN throws a nasty error (the Microsoft.Owin 2.0.1.0 assemblies were copied to the Web Project bin folder).
To fix I had to "update-package Microsoft.Owin -version 2.0.2.0" on the out-of-date project, clean and rebuild everything.
UPDATE:
Still getting the same problem. I assume now that it's some incompatibility issue between SignalR 2.1.0 and Owin 2.0.2.0.
SturmUndDrang
Updated on July 09, 2022Comments
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SturmUndDrang almost 2 years
I have a Web API project that uses SignalR which started giving me "unable to find Microsoft.AspNet.Signal.Core" errors frequently which were only fixed by doing a full rebuild in Visual Studio.
I upgraded SignalR and OWIN in Nuget to try and fix this issue, but now I always get "The following errors occurred while attempting to load the app. - No assembly found containing an OwinStartupAttribute. - No assembly found containing a Startup or [AssemblyName].Startup class"
I am the only person on my team to get this error - the same code works fine on other machines.
I have a Startup Class:
using System; using System.Collections.Generic; using System.Linq; using System.Web; using Microsoft.Owin; using Owin; [assembly: OwinStartup(typeof(MyProject.Startup))] namespace MyProject { public class Startup { public void Configuration(IAppBuilder app) { app.MapSignalR(); } } }
I have tried adding the AppStartup key to the web.config too:
<add key="owin:appStartup" value="MyProject.Startup, MyProject" />
I have the following references in my WebApi project:
Microsoft.AspNet.SignalR.Core (2.1.0.0) Microsoft.AspNet.SignalR.SystemWeb (2.1.0.0) Microsoft.Owin (2.0.2.0) Microsoft.Owin.Host.SystemWeb (2.0.2.0) Microsoft.Owin.Security (2.0.2.0) Owin (1.0.0)
I'm using IIS 8.5 on Windows 8 64Bit
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AdamC over 7 yearsThanks! This fixed it for me.