exec(),System(),passthru() don't work in NT 4

Hi. We have a problem executing commands in our NT system. We have tried to work with exec,system and passtrhu commands but none of them make any change. We have tried several things like: exec("dir c:\\"); exec("c:\\winnt\\system32\\cmd.exe dir c:\\"); exec("copy c:\\temp\\filea.txt c:\\temp\\fileb.txt"); and we have given all possible permissions to the directories involved. Our system uses a load balancing system that comes with site server. Other machines without this configuration work correctly. Can anyone help us? Thanks