You may have an outdated version of the C# client installed. Check and update if necessary.
I updated the vSphere client but I am still seeing the same result. I downloaded version 6.0 of the client, which is the same version of ESXi I am using. is there any log or output other than the 504 error code that could indicate where the problem is?
I am trying to use the client on a VM running inside the same ESXi host I am trying to connect to, does that matter?
A 504 is a specific response code that usually indicates a form of networking issue. Can you ping the ESXi management vmkernel interface and, if so, what RTT are you seeing? Can you try from another system on the same subnet?
It was a networking problem although only using the client, no ping or http. The problem was that the vm had a web proxy configured and was trying to contact the esxi host through that.
The RTT was the right pointer. Thanks!