UPDATE - Please look at my answer for a link and explanation of the solution to this problem
Before we start, I know this is a very common quest
I tried all these solutions, but none worked.
This is how I resolved it: Deleted all my temp asp.net files. After I'd done this, I got new config errors. I fixed them. The last, and real error came out: new Bootstrapper() was trying to load an older version of a ninject dll. Removed all ninject packages. Installed ninject nuget packages one by one, make triply sure that the correct version is installed.