Find/Given using programming toolbar - it only works intermittently

I'm using code off of a project partner where he laid out a find/given function using the programming feature. In most instances it works, however when I change a variable value or add a variable to the equation, it goes "undefined" and will no longer give me an answer. This seems work well when we did the original calculation sheet, however, when I go and try to make revisions to it there are problems that always occur.

Even when I just copy and paste the parts to another worksheet it stops working.

I didn't want to redo his entire worksheet using another method to find the answers. Does anyone know why I would keep having problems with this method? Is there some syntax that is very discrete that I'm missing? If not solving through this method, do you have a recommendation?

Thanks,

Nick