MUPad ode::solve error shows not an ODE

I am trying to solve the partial differential equation (Kindly see the attached files from line1.jpg) using MuPAD but I am stuck on the last line(In image line3.JPG) where it shows equation is not ode but the U(z) is only function of z so it should solve it as ode since it is

(The other files Line1 , Line 2 are screenshots of the code from the first line)

[Torsten]

I don't understand why you consider r - it cancels out.

[dev burman]

Could you please tell which line are you talking about? (Is it in Line3.jpg ?)

[Torsten]

I mean the line for de2 (i.e. the line before the error occurs).

[dev burman]

you mean I should write ode::solve(de2*r,U(z))? instead of what i had done. But its still shows the error