Injecting into constructor with 2 params is not working

Check the IAppCacheimplementation CachingService to make sure that the class is not throwing any exception when initialized. that parameterless exception is the default message when an error occurs while trying to create controllers. It is not a very useful exception as it does not accurately indicate what the true error was that occurred.

You mention that it is a 3rd party interface/class. It could be requesting a dependency that the container does not know about.

Referencing Unity Framework IoC with default constructor

Unity is calling the constructor with the most parameters which in this case is...

public CachingService(ObjectCache cache) { ... }

As the container know nothing about ObjectCache it will pass in null which according to the code in the constructor will throw an exception.

UPDATE:

Adding this from comments as it can prove useful to others.

container.RegisterType<IAppCache, CachingService>(new InjectionConstructor(MemoryCache.Default));

Reference here Register Constructors and Parameters for more details.

Most of the DI containers while trying to resolve a type always look for a constructor with maximum number of parameters. That is the reason why CachingService(ObjectCache cache) constructor was being invoked by default. As ObjectCache instance is not registered with Unity, so the resolution fails. Once you force the type registration to invoke specific constructor, everything works.

So if you register IAppCache and force it to invoke CachingService() - parameter less constructor, it will work as expected.

container.RegisterType<IAppCache, CachingService>(new InjectionConstructor());

Registering it this way, will force the parameter less constructor to be invoked and internally it will fall back on whatever the third part library wants to use as default. In your case it will be

CachingService() : this(MemoryCache.Default)

Another option that was mentioned in other answers is to register and pass the constructor parameter your self.

container.RegisterType<IAppCache, CachingService>(new InjectionConstructor(MemoryCache.Default));

This will also work, but here you are taking the responsibility of supplying the cache provider. In my opinion, I would rather let the third party library handle its own defaults instead of me as a consumer taking over that responsibility.

Please take a look at How does Unity.Resolve know which constructor to use?

And few additional information for Niject https://github.com/ninject/ninject/wiki/Injection-Patterns

If no constructors have an [Inject] attribute, Ninject will select the one with the most parameters that Ninject understands how to resolve.