Vsphere Client 6.0

[JPbalean23]

Hi 

We are experiencing An unknown connection error occurred. (The Client could not send a complete request to the server  (The underlying connection was closed: An unexpected error occurred on a send)).

ESXi Version: 7.0 U3

VSphere Client Version: 6.0

is this a compatibility issue or network-related?

Thank You

[miladmeh8]

the vsphere client cannot connect to ESXi version 7 . it is not supported

[scott28tt]

Point a web browser at the ESXi 7.0 host.

[VRO123]

vCenter Server 6.0 cannot manage ESXI 7.0
vCenter Server 7.0 can manage ESXi version up to 6.5 hosts in the same cluster as ESXi 7.0 hosts. 
vCenter Server 7.0 cannot manage ESXi 6.5 or earlier hosts.

vSphere supports upgrades from vCenter Server 6.5 and later to vCenter Server 7.0. To upgrade from vCenter Server 5.0, 5.1, 5.5, or 6.0 you must first upgrade the vCenter Server instance to version 6.5 or later releases, and then upgrade to vCenter Server 7.0. 

in your case it is a compatibility issue! You can use ESXI as a standalone host!