Solved a combined error 1618 + 1603 for two Win10x64 v1903 (May 2019 build) by enabling the Windows Feature "Windows PowerShell 2.0 Engine" - I really was missing PowerShell 1.0! (and 2.0).
Heres a quick guide for what fixed it for me:
Goto "Control Panel" --> "Programs and Features" --> "Turn Windows Features on or off" (left side, you can also just type this into Start) --> FIND & CLICK CHECKBOX FOR: "Windows PowerShell 2.0" (near the bottom) -> this should have only one item under it, "Windows PowerShell 2.0 Engine", which gets checked when you check the parent category --> Click OK/etc. to save & close
After that, I went back to my previously downloaded installer from LastPass' download page @ [ https://lastpass.com/misc_download2.php
] - The installer went-through just as it normally does. Maybe the new build of windows is finally not including older versions of PowerShell by-default?
Either way, hope this helps. Cheers.