mpich-gm hangs for >=128 size messages

Hello,

MPICH-GM seems to hang for messages 128 bytes and larger over Myrinet.
I can only get MPICH-GM to work for 64 byte messages and smaller.  
If I run MPICH-GM over shared memory the problem does not occur. 
MPI-LAM works for the *same* program over TCP for large messages 
and shared memory.

Any ideas how to fix this problem for MPICH-GM?
I am only using simple send and receives i.e.:
      
      MPI_Recv( msg, count, MPI_CHAR, nodeid, tag, MPI_COMM_WORLD, &st);
      MPI_Send( msg, count, MPI_CHAR, nodeid, tag, MPI_COMM_WORLD );
 
BTW:
 
gm_allsize runs ok for large messages, the problem seem to only happen with
MPICH-GM over myrinet.
 
Any help is appreciated.
 
Thanks,
 Maria