I’m running Postgres 9.1’s pg_ugrade to migrate from 9.0 to 9.1 on Windows x64. After editing the permissions to allow full trust, running the tool as the postgres user, and working around a bug whereby pg_upgrade leaves the "old" store locked and refusing to run again ("there seems to be a postmaster servicing old cluster"), it now fails without explaining what’s wrong:
Performing Consistency Checks
-----------------------------
Checking current, bin, and data directories ok
Checking cluster versions ok
Checking database user is a superuser ok
Checking for prepared transactions ok
Checking for reg* system oid user data types ok
Checking for contrib/isn with bigint-passing mismatch ok
Creating catalog dump ok
There were problems executing ""C:\Progs\Postgres\9.0\bin/pg_ctl" -w -l "nul" -D "C:\Progs\Postgres\9.0-data" stop >> "nul" 2>&1"
Failure, exiting
Is this tool production-ready or am I wasting my time? If this is what I should be doing, what are your suggestions for solving the current failure?

postmaster.idfile in your directory that you need to delete. – Phrogz Feb 23 at 23:26