M630 Mezzanine Nic Issues

Hi i have 4 esx hosts built on m630 blades.Two of which work fine and two are giving me packet drops only on VMNIC4 which connects to the B1/B2 fabric of the enclosure. This setup works fine on the other two connected to the same fabric, switches, bladecenter etc.  i tried different slots and dell sent me a new Mezz card which has to effect.  It's only that one vmnic though which is strange. any help would be great