Why do I get an Array dimensions mismatch error, using a graphical function in Stateflow (c AL)?

Input is a vector of 10 and I try to access the entries with a for-loop.

Example: output = input[k];

It works fine, if I excecute the same stateflow fuction in a substate

y_temp = y_temp*(x_h-xi_h)+param[i];

^^^^^

Array dimensions mismatch for data 'param_h'.