Hi Mario!
>FATAL 1: postgres: could not locate executable, bailing out...
seems to me, that the user, you are starting postgres as, cannot find some executable. Make sure, all Postgres binaries are reachable via PATH. (issue echo $PATH on the commandline to see the current paths, if you're using a Un*x).
If this doesn't help, try increasing the debuglevel (-d 5) and see, if the postmaster gives you a hint of what file it can't find.
HTH,
Stefan