Multithreading - std::mutex issue in C++ / CLI

I've seen quite a few links about this, however none of them seem to be specific to me and have a lot of concerning gaps. Take this link here for example, What is the alternative to futures and promises in managed C++ it is said that you cannot include <mutex>, <future>, <thread> yet this isn't technically the case for me, I can include all of them. I've even gotten std::thread to work perfectly, which is why I am here. I get to needing to use std::mutex, however after including it, it tells me that mutex is not a member of namespace std after declaring some variable of type std::mutex.

What are my options for achieving the same thing as multithreading with mutex that I can in a normal C++ application that I now can't in a C++ / CLI one?