Hi Erez,
Thanks for the reply. Admittedly the server had to go into production running the original version of OFED (1.5.3-4.0.42). IB works fine on this server/network switch configuration.
I'm not familiar with PFC. However I can see the following setup in the existing node (running the older version of OFED):
options mlx4_core pfctx=0 pfcrx=0 log_mtts_per_seg=6
I originally tried re-installing the driver again with the same effect. As for the switch I'd have to check with the network administrator.
In any case I may revisit the problem at a future time.