I have an old ASP.NET Web API 2 which I would like to update with OWIN. As usual, it didn't go smoothly.

After updating to OWIN, it somehow threw a 404 error. I spent hours trying various things as stated below but none works.

• Verified the order of route registration
• Attempted to use Route attributes
• Applied runAllManagedModulesForAllRequests="true" on modules tag in web.config
• Made sure spelling, Nuget packages and imports are correct
• Checked with a brand new Web API project to make sure code are correct

At the end, I remembered that I accidentally hit "Create Virtual Directory" when the Project Url field was set to "http://localhost:xxxxx/api" and using IIS Express. I suspect the virtual directory was the issue. After few online searches, I found the virtual directory was set in:

<solution folder>/.vs/config/applicationhost.config. 

Removing the virtual directory solves my 404 issue.