convert open loop NARX to closed loop

hello every one

i have a question which is vitally important for me.

i have trained a series-parallel NARX neural network by nntool in matlab and now i want to convert it to

close loop one.

i read in HELP that i should use closeloop(net) for this purpose but when i used this code

nothing happens . there is no error but the nework is still an open loop network .

i have no idea how i can solve this problem .

i will be gratefull if you help me.