Error at installing 12.16

When installing 12.16 over 12.15 I get Directory%20Opus%20install%20error%202019-07-30 an error message "unhandled exception error number 0x800FFFF" and it's impossible to install 12.16. I diabled my antivirus program (Kaspersky) to no avail.

What's next?

This seems to be a Windows 10 bug which has affected some people, and also has turned out to affect installers for other software, not just Opus. Windows* is telling the installer it is a 32-bit system when it's a 64-bit system, for some unknown reason. (*Or something else. A lot of affected people seemed to run CCleaner, but that may be a coincidence.)

The best known fix anyone has found so far is to create a new, temporary account in Windows and run the installer from there. That will then work, and upgrade Opus in both accounts.

The people who had the problem in the past haven't come back since trying and confirming that fix, so it looks like it may also fix whatever is wrong with the main account as well, such that later updates may work without having to use the other account.