The issue seems to be that you have probably not created a machinefile which consists of node name to number of processes mapping and this file should be present in the same dir. of the other nodes on which you are launching other MPI processes, this is required in case you want to run the MPI program across the two or more nodes, you can find more details of the format in which this information has to be in the machinefile and the other requisite steps need for running your MPI program across multiple nodes from this link
http://wiki.mpich.org/mpich/index.php/Using_the_Hydra_Process_Manager Also, in order to launch the processes across multiple nodes you need to do ssh passwordless login among those nodes, in case you are using ssh as the connection mechanism, you can find more details about the procedure for ssh passwordless login over here
http://www.techlitic.com/ssh-passwordless-login.html