This error message started showing up during testing of some code changes I made to an application. It took me awhile to figure out precisely what the problem was because the top of the stack trace referred to this:
System.Activator.CreateInstance[T]()
As looked further down the stack trace, it ultimately pointed out which class was the culprit, so I added an empty public constructor to and redeployed the result.
I found this post rather useful in diagnosing the problem.