I am getting an error after upgrading a project to .net 4.6.1, though it can be recreated.

To reproduce:
Create a new MVC project.
install-package infragistics.web.mvc
add a view

In the view add:

@using Infragistics.Web.Mvc

<section class="row">
@(Html.Infragistics().Grid("reportgrid", Model.GridModel))
</section>

Intellisense will even suggest Infragistics(). If you mouse over Grid() it shows the helper method header, however after a few moments Infragistics is underlined and shows the error:

"HtmlHelper<T> does not contain a definition for 'Infragistics' and no extension method 'Infragistics' accepting a first argument of type HtmlHelper<T> could be found (are you missing a directive or assembly reference?)".

The project will compile but then throws the same error at runtime if you hit the view. This worked with a much older version of Infragistics.Web.Mvc (v2.x) and in an older version of MVC. It seems odd to me that it compiles and also intellisense suggests it but it then errors.

Am I missing something? Im not sure how to fix this in the upgraded project, any help is appreciated.