What OS are you running? I would suggest referring to http://www.ni.com/support/gpib/versions.htm to make sure that you have the latest driver installed. Once verified, do the GPIB test utilities (Getting Started Wizard, ibtsta, ibdiag, etc) recognize the ENET? Are you able to find listeners at the instruments' addresses using IBIC? Make sure that you keep the bus to 488 specifications. I would suggest, for testing, that you connect only one instrument (powered on) to the ENET with a maximum of 2m of cabling.
