For some reason, the Save PDF to Web Receipts Folder workflow is incompatible with FileVault -- it gives an error when you try to run it.
Whatever the underlying problem is, it's the New Folder action in that workflow that's incompatible with FileVault. One fix is to make a copy of the workflow (which lives in /Library » PDF Services), open it in Automator, and replace the New Folder action with Copy Finder Items.
I'd also suggesting adding the fixes from this recent hint, to prevent the overwriting of items in the web receipts folder, while you're in there with Automator.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070213163443233