Without going into details it's hard to say what's causing the issue. Maybe the network issue is just a result of other issues. Anyway, I'd stay with ESXi 4.1 as long as the host is still connected to the EVA. I'm currently doing a migration with a customer from an EVA 4000 to a new 3PAR 7200 and we are going to keep the hosts at version 4 for the migration (we planned to use HP's SAN Copy utility as well as Storage vMotion) and upgrade them once the LUNs/VMs are all on the new storage.
André