I have looked through other posts but none seem to answer what I need.
In my case the culprit was the fact that Global.asax was placed under the '/Views' folder. This was somehow working while the project was targeting MVC3. Once the solution got upgraded to MVC4, running said solution would result in the aforementioned errors. In a similar vein, other errors would crop up mentioning:
"no default webpage has been set and directory browsing has been disabled"
The solution: After upgrading to MVC4+ I had to manually move Global.asax under the root folder of the container project. Be sure to inspect Global.asax to make sure that the namespace applied within is the proper one. Just my 2c.