Encountered an unexpected error when attempting to resolve tag helper directive '@addTagHelper'

I'm using Visual Studio 2015 Community edition, and I've created an ASP.NET MVC 5 project.

When I open a view (Index of Home or any other), it shows first three lines of the page underlined with red as a syntax issue. Here is the error:

> Encountered an unexpected error when attempting to resolve tag helper > directive '@addTagHelper' with value 'Microsoft.AspNet.Mvc.Razor.TagHelpers.UrlResolutionTagHelper, Microsoft.AspNet.Mvc.Razor'. > Error: Object reference not set to an instance of an object

The screenshot:

When I build the project, it build successfully. When I run it, it shows a lot of errors, but it runs the application.

> The type or namespace name 'Mvc' does not exist in the namespace > 'Microsoft.AspNet' (are you missing an assembly reference?)

and

> '_Page_views_home_index_cshtml.ExecuteAsync()': no suitable method > found to override

How can I get rid of this?

Here's how I fixed the issue:

First, reset the Visual Studio Component Cache by closing Visual Studio and deleting this folder: > C:\Users\[Username]\AppData\Local\Microsoft\VisualStudio\14.0\ComponentModelCache

And finally, check the web.config files and change:

<appSettings>
    <add key="webpages:Version" value="2.0.0.0" />
    ...
</appSettings>

to

<appSettings>
    <add key="webpages:Version" value="3.0.0.0" />
    ...
</appSettings>

I had the same problem, but the above didn't work. I also deleted all 4 files in the Component cache which didn't work. I noticed that the line below <appSettings> was set to false. I changed it to true and the red squigs were gone.

<add key="webpages:Version" value="3.0.0.0" />
<add key="webpages:Enabled" value="false" />

In my case it was the reference to System.Web.Mvc had disappeared.

There was lots of errors in the cshtml files but it would compile and run. Then I found that I had an error in the xxxcontrollers.cs file trying inherit controllers.

Seems it could compile because the dll was in bin already but it was giving errors.

I did not relish having to rebuild this project. That would be days and days.