I had this issue despite having all the correct configuration.
It turned out to be some bad files in the Component Cache, preventing the Razor views from recognising ViewBag, Model, and HtmlHelpers. Deleting these files solved the problem (good versions of these files were created next time I opened Visual Studio).
The files are located here:
%LOCALAPPDATA%\Microsoft\VisualStudio\14.0\ComponentModelCache
Delete all four files:
- Microsoft.VisualStudio.Default.cache
- Microsoft.VisualStudio.Default.catalogs
- Microsoft.VisualStudio.Default.err
- Microsoft.VisualStudio.Default.external
I have subsequently seen the same issue on several other developer machines and this fix quickly solves it.