BUG #5690: pg_upgrade fails

The following bug has been logged online:

Bug reference: 5690
Logged by: Tony marston
Email address: tony(at)marston-home(dot)demon(dot)co(dot)uk
PostgreSQL version: 9.0
Operating system: Windows XP
Description: pg_upgrade fails
Details:

I am trying to upgrade from version 8.4 to 9.0, but when I run pg_upgrade it
fails with the following error:

"Creating catalog dump Access is denied"

There were problems executing "f:/postgresql/9.0/bin/pg_dumpall --port 5432
--username "postgres" --schema-only --binary-upgrade >
"C:\WINDOWS\system32\pg_upgrade_dump_all.sql"

How can this be? If it's running as superuser then surely it has automatic
access to everything!!!