how to pass a vector as an input to level 2 matlab s function?

i am having a function file as

function y=fs(u)

1. but my input u is an output of a mux. it is a column vector. so i have converted it as a row vector by using the code u1=u'.
2. when i run the file i get the following error. error evaluating initialization for matlab s function.
3. when i want to see the value of u1, the following comes.u1= Simulink.MSFcnRunTimeBlock.

Is it possible to pass a workspace variable as a parameter to this s function.