Can't install SB 4.18 "Can't delete registry key 0x80000002"

[Brent G]

I am trying to install Sandboxie 4.18 on top of my existing 4.16 version. "Overwrite (upgrade) the existing installation".
I am using Win 7 Ultimate 32 bit SP1.

The install program SandboxieInstall.exe starts up ok, but after 10 seconds it says (msg above the progress bar) "Can't delete registry key 0x80000002 Software\Microsoft\Windows\CurrentVersion\UnInstall S..". I can't see what the full registry key is because the Windows dialog truncates it. The progress bar does not move and the message above the progress bar does not update.
The install program just sits there forever. I tried installing with administrator rights but same thing happens.

Is there a solution?
TIA
Brent