access method 'System.Web.Http.HttpConfiguration.DefaultFormatters()' failed

Try ensuring that Microsoft.AspNet.WebApi.Client is installed.

My app wasn't working because I'd removed that for other reasons.

Open Package Manager Console and execute:

Install-Package Microsoft.AspNet.WebApi.Client

Check your packages.config , Make sure that the following Nuget packaged libraries are at the same version:

<package id="Microsoft.AspNet.WebApi" version="x.x.x" targetFramework="net45" />
<package id="Microsoft.AspNet.WebApi.Client" version="x.x.x" targetFramework="net45" />
<package id="Microsoft.AspNet.WebApi.Core" version="x.x.x" targetFramework="net45" />
<package id="Microsoft.AspNet.WebApi.WebHost" version="x.x.x" targetFramework="net45" />

Uninstall-package from WebApi, WebApiWebhost, WebApi.Core, WebApi.Client

PM> uninstall-package Microsoft.AspNet.WebApi
PM> uninstall-package Microsoft.AspNet.WebApi.WebHost
PM> uninstall-package Microsoft.AspNet.WebApi.Core
PM> uninstall-package Microsoft.AspNet.WebApi.Client

Reinstall-package,

PM> install-package Microsoft.AspNet.WebApi -version x.x.x

Make sure that the following Nuget packaged libraries are at the same version:

Microsoft.AspNet.WebApi
Microsoft.AspNet.WebApi.Client
Microsoft.AspNet.WebApi.Core
Microsoft.AspNet.WebApi.WebHost