This is a quick one that will, hopefully, save someone out there an hour or two! Recently I was doing deployment and I came across this error:
I tried all the usual IISREST, clean the temp .NET files a reboot but nothing worked until I realized what had happened... I did some cleaning on the server and had 'cleaned' the 'Bin' folder. When I did my next deploy, some of the core EPi assemblies had not copied over correctly because some of the assemblies were set as 'copy local' set to true. When I did my deployment, the EPi core assemblies were missing and the error occurred. Fix: Make sure you have all your core Episerver DLL's included in your build!