Hi Robert,
Work-around: open Git Bash once as an administrator.
This _should_ have been done as part of the installation (a hidden Bash is
run as administrator at the end), but apparently that is not working...
To help diagnose this, maybe you can run the installer using the
`/LOG=<filename>` option and inspect the log whether it contains any
obvious hint as to what went wrong?
Ciao,
Johannes