Muti step ahead prediction using closed loop NARX problem!!

Hello,

I am working on a multivariate time series forecasting task for which i have trainned a NARX network which gives me quite good results,after training the model from nntool i export the model which i assumes is the open loop model,now for multistep ahead forecast i convert it in closed loop NARX but the performace for this model is drasticaly bad.How i can forecast with such poor model kindly help me in this regard.

1)How the close loop model performance be improved?

2)How i can use my close loop model to forecast the unknown targets?