This error can arise when MPICH2 is installed without the proper admin privileges.  When that happens, the SMPD service that MPICH2 needs to run does not get started, so MPI jobs raise this error and fail.  Please check the status of the SMPD service, called mpich2_smpd in Task Manager, and make sure it is running.  If it’s not, try to start it manually.  If that doesn't work, it may require an uninstall/reinstall to get it to work correctly.