Are you able to ping the iSCSI vmkernel port from the NetApp and vice versa?
on the CLI of an ESX Server
vmkping -I vmkX x.x.x.x
In case you have Jumbo Frames configured, use
vmkping -I vmkX -d -s 8972 x.x.x.x
on the NetApp CLI:
net ping -lif <lif_name> [-packet-size 8972] -destination <iSCSI-vmkernel-port>
Peter