incremental conductance with daq problem

i used incremental conductance method to control dc-dc converter to get maximum power of photovoltaic cell . i interface it with NI data acquisition card but it stopped working after a few m seconds and it gives message error "nan infinity of error "and it stops . i will attach simulink file for this algorithm . it is working in simulation very well . the error value reached -inf and there is no change of current or voltage.