That's very strange. What happens if you run with "-mca
btl_tcp_if_include en0,en1", which will use both devices. The fact
that the exclude option doesn't work makes me wonder if there isn't
another device that appears active somewhere in the cluster. The
most likely suspect on an OS X cluster is a firewire device that
somehow has sprouted an address and gotten marked as active. You
might want to run "ifconfig -a" on all your nodes and make sure the
output is mostly the same.