Two users have reported that after updating to Lion 10.7.4, downloaded script applets from this site would bounce in the Dock when launched and would not open. It turns out that the users had previously disabled the quarantine system. This normally alerts you when a new application or document has been downloaded from the internet as you are about to open it for the first time. For some reason this setting was not picked up in 10.7.4or somethingand logs an error like this to Console.app:
posix_spawn("path/to/the/app",...): Operation not permitted
Topher Kessler has an article at cnet (published before this 10.7.4 issue arose) that explains how the quarantine setting works and how you can reset it in order to get the downloaded apps running correctly.