I have encountered this problem much sooner than I thought. I cant seem to access this VCenter system using Vsphere 6. The error is: An unknown connection error occurred. (The client received an invalid response from the server. (The server committed a protocol violation. Any ideas? I've tried using the web UI but I cant seem to make any sehnse of it. I can find list boxes and a good fewbuttons. Once I moved to hosts and clusters. However, I cant get to the tree view for VM's. I'm in a bit of a bind. I need to provision two servers today. I have no idea what I'm going to do. Maybe I could connect using powershell? I must look into that. TO provision the servers, I first need to explore the data stores and networks on this cluster so I know where to put this VM. As someone here likes to say, I'm bunched! Any help very appreciated. Darragh P.S. All the VSphere downloads are here: https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2089791