Hi Yujin,
when using Windows HPC server 2008, you already have MPI, i.e. MSMPI. it is part of HPC server 2008. The related MSMPI binaries are under %ccp_home%\Bin (mpiexec.exe, smpd.exe, msmpisvc.exe etc)
1) You cannot mix MPICH2 with MSMPI.
2) HPC scheduler doesn't support MPICH2 by default. So running any MPICH2 MPI with HPC scheduler will fail.
3) about "mpi.dll", MSMPI doesn't have this dll. it seems like froming MPICH2. If your MPI.exe are built with MPICH2, please rebuild it with MSMPI SDK.
Hope this helps,
Liwei