Hello mryellow!
Yesterday I tried the the unsupported fix which grasshopper suggested and it worked for me too. Image may be NSFW.
Clik here to view.
After I've replaced the hash string and restarted vCenter Server, the installation of vSphere Webclient with the new set password finally succeeded.
To all a big thanks, especially to grasshopper... Image may be NSFW.
Clik here to view.