I take it you mean the vSphere Client (not vSphere). The C# client is old and dead and not compatible with Windows 10. If you need to manage ancient ESXi hosts with said client you'll need an older version of Windows.
Yes, I meant vSphere Client. I would agree with you, but I have already installed this without issue on another Windows 10 machine and it works perfectly. So I am not sure why this new machine (brand new out of the box, same make & model as the one that is working) won't work.
I've seen this issue two, and what solved the issue in my case, was to simply install a newer vSphere Client version - which installed the .NET binaries correctly - and then install the vSpehere 5.5 client. For download links, see https://kb.vmware.com/s/article/2089791
I tested installing a newer version (6.0) and it still gave me the same error. What ended up working was me just wiping the system completely and rebuilding Windows 10 Pro. Once that was done, it installed on the first try. Must have been a bad build.
Thank you all for your help!
I had the same problem with 2 brand new HP laptops and vSphere Client 6.0 and Windows 10 Pro (1803) this week.
I installed one in October without any problem, so I compared them and there was 2 newer Microsoft updates on the new laptops, KB4465663 and KB4477029 since I ran Windows Update before I tried to install vSphere Client.
I did a factory restore on one of the new laptops today and installed vSphere Client 6.0 as the first thing and there was no problems, so I suspect that one of the updates was the reason to the problem.