non-linear ODE

Hello,

I try to solve a highly non-linear 2nd order ODE, like the example enclosed, example I found on an old answer into the old FAQ.

As long as I just execute this file into Mathcad 14, no problem.

But when I want to modify it with my own conditions and limits, the whole file doesn't work again, the functions definitions and particularly the rkadapt appear in red with the comment "cannot be used here".

I also notice that the number of arguments of rkadapt is larger (2 more) than described in the help files...(?)

Are there a way into Mathcad to solve these kind of high non linear systems for a real job, not academic (when we do not know the solution before, and so cannot choose the "right" initial conditions) ?

Thanks for your help

Pierre