Ошибка:
The vSphere Client could not connect to vCenter server. The server vCenter server took too long to respond. (The command has timed out as the remote server is taking too long to respond.)
Решение:
Как вариант перезапустить все сервисы на vCenter Server 6.х
service-control –stop –all
service-control –start –all
https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2109881