I get this error on a 7.3 build:

The following errors occurred while attempting to load the app. - The OwinStartupAttribute.FriendlyName value 'UmbracoDefaultOwinStartup' does not match the given value '' in Assembly 'umbraco, Version=1.0.5750.18164, Culture=neutral, PublicKeyToken=null'. - No assembly found containing a Startup or [AssemblyName].Startup class. 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.

Any ideas? I've even removed owin.dll and the reference from the solution, also added to the web.config and get the same error?

Thanks