We are attempting to upgrade Postgres 10.10 to 12.4 using pg_upgrade on a Windows 2016 Server machine using the command


```
> "C:/Program Files/PostgreSQL/12/bin/pg_upgrade.exe” --old-datadir "C:/pgdata/10/data" --new-datadir "C:/pgdata/12/data" --old-bindir "C:/Program Files/PostgreSQL/10/bin" --new-bindir "C:/Program Files/PostgreSQL/12/bin"
```


It fails with the error

>   
> could not get pg_ctl version output from "C:/Program Files/PostgreSQL/10/bin/pg_ctl" --version Failure, exiting


Running pg_ctl – V from the command line correctly identifies version 10.10.

This is on a sandbox machine but both installs have been tested and are connectable, writeable and readable.
The command is being run under the ‘postgres’ Windows user from an empty, writeable directory.
Both Services are stopped.

I haven’t had any success Googling the error, so does anyone know the cause and how to get past it?

Thank you