Cannot compile with an enpty func in header file

So, I create new project for clear. Then I create new C++ class based on ACharacter engine class. In header file i create function prototype for example void Jump(float a) and its works great, but when I create function prototype without input parameters for example void Jump() - I have compile errors.

What interesting! Its works when func. prototype have input parameters, or it works when we create an empty body for func. with no inputs in .cpp file.

How it does not work? what error do you getting? can you paste what you got in Output tab? (please dont use Error List)