Question: initial condition error

Hi everyone 

I solve several differential equations using dsolve. Now I want to change one initial condition a little bit: 

before: u0n := u0*ms/(ms + mn)

new: u0n := u0*ms/(ms + m(t)

When solving the new system I am getting the error message: Error, (in dsolve/numeric/process_input) unknown piecewise(0 < 16-(xn(t)^2+(zn(t)-16)^2)^(1/2), 16-(xn(t)^2+(zn(t)-16)^2)^(1/2), 0) present in ODE system is not a specified dependent variable or evaluatable procedure

I am guessing this has to do with a function in an initial condition. 

Has anyone an idea how to solve this problem?

I added the maple file for the whole overview.

Thanks in advance!

Please Wait...