Question: How do I solve the Error, "invalid input: rhs expects 1 argument, but received 2"

Hello.

I wrote some codes for solving equations in a special way. My codes work very fine when my differential system has only one equation.

But when I extend it to a system that has two or more equations, sometimes does not work and I face with error. However, in one system (2 eq) it also works. But it is only a special case. If you want, I can upload it here as well.

I am attaching the maple file containing the error. You can observe it. 

By examining many cases, I think that maybe the root of the problem is that I must change my codes in a way that they are for a "system". Indeed, instead of writing codes for each differential equation, I must define a system and write these codes for a system containing some differential equations.
However, I think that the boundary conditions sometimes also may be the root of the error.

I change the attached codes for this purpose, but I failed. I prefer to not present my wrong codes for this purpose. 

If it is possible, help me to change my codes.

Thanks a lot.

ERROR.mw