You might get this error when setting up a new Sitecore instance somewhere. The item in question is a /sitecore/layout/Devices item that Sitecore needs in order to operate normally. There can be several reasons why this is happening: You are running Sitecore up to 9.x, and your master / web databases are
I was setting up my Sitecore instance(s) on a new laptop, when this error reared its ugly head and kept me stuck for a good hour. Looking online there are many reasons why this showed up, but in my case, all I had to do was adding this line under configuration/system.web/compilation/assemblies:
Just a very quick write-up on this as it kept me busy for a couple of hours looking for a solution. After upgrading a number of NuGet packages (Microsoft ASPNet WebApi 2.2 Core Libraries, Microsoft ASPNet MVC, HtmlAgilityPack), my perfectly working Sitecore local development setup stopped working, instead throwing the