Hello everyone, I'm a new user to Mathematica and i have been trying to solve my equations using Explicit Runge-Kutta Method. The problem is that I have encountered "stiffness" problem, which shouldn't happen according to the calculation.

At first, I need to solve this equation by using 4th Order Runge-Kutta Method, but, it seems like Mathematica have a build it package (Explicit Runge-Kutta Method). I tried to use it and problem occur. Can anybody advice on what is the problem?, Should it be my own equation missed out something?