I (in collaboration with a friend of mine) found out that COPS on Windows (7) and a WAMP server will only work if the calibre directory is in the path of the COPS installation.
(1) (set path in config_local.php)
(2) (set path in config_local.php)
will work, while
will NOT (under Linux this is not a problem)
To make the second example work under Windows (7) with an Apache server you need to create an alias, otherwise apache cannot find COPS in the z:/ebooks/cops directory.