Thank you for reply.
An attempt of the clean installation.
I've uninstalled Resolve and removed folders "Blackmagic Design" from
C:\Program files*\
C:\ProgramData\
C:\Users\Public\Documents\
C:\Users\%USERNAME%\AppData\Roaming\
C:\Users\%USERNAME%\Documents\
Then ran installation.
DaVinci_Resolve_16.0b3_Windows.zip
1582325919 bytes (1509 MiB)
CRC32: 46467C0E
DaVinci_Resolve_16.0b3_Windows.exe version: 16.0.0028
"Unable to load plugin" window is here again.
Trace shows the same searches:
After copying openvr_api.dll into ..\ the alert window is gone.
Probably, it is not an installation app fault, but the OS. I use Win7 Sp1.