Sounds like your Launch Services database is screwed. Try rebuilding it:
http://hints.macworld.com/article.php?story=20071102084155353
If you don't want to do it through Terminal, you could use Cocktail or Yasu to do it.
Oct 2 10:19:12 S2L-Studio installd[225]: PackageKit: Executing script
"./postflight" in /private/tmp/PKInstallSandbox.sfVcYw/Scripts/
com.growl.growl.pkg.ZWKbzN
Oct 2 10:19:13 S2L-Studio installd[225]: ./postflight: 2010-10-02
10:19:12.998 OpenDocWithoutAddingToRecents[422:903] Couldn't launch /
Library/PreferencePanes/Growl.prefPane: LSOpenFromURLSpec returned
-10814/E.g. no application claims the file
I think it's having a problem with the after install portions even
finding things on disk. Can you check your home directory and see if
the prefpane landed there somehow? Check in /Library/PreferencePanes
as well.
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Huh?
> Does it make a difference that my startup disk is an SSD, but my user directory is has been moved to another disk?
Nope. My Home folder is on another partition as well. It's on the same physical disk, but that shouldn't matter.
If the prefpane were in the wrong place, either the script would be complaining about the path where Installer had put it, or the script would be complaining that it couldn't find the file at that path. You'd most likely see -43 (file not found), not -10814.
> Check in /Library/PreferencePanes as well.
It'd be worth checking not only whether the prefpane exists there, but what Finder says in its Info window about what application will open it.