When I added an extra SCSI card to my ESX 3.5 test system I could not get it to reconnect again with VirtualCenter. After a close inspection I noticed that vmnic0 did not exist anymore(esxcfg-nics -l), it got renamed to vmnic1. Because of that my vSwitch0 did not have a NIC linked to it anymore. I linked the new vmnic1 to my vSwitch0(esxcfg-vswitch vSwitch0 -L vmnic1) and everything was up and running again. I’m glad this didn’t happen in a production environment with several vSwitches and portgroups, than again it is possible to rename them again by manually editing the /etc/vmware/esx.conf file. There’s a knowledge base article on this behavior on the VMware support site, I noticed it a couple of weeks ago an now I witnessed it. Definitely not the first place I would normally look. I hope VMware can fix this glitch, although I can fully understand why this happens.