My Applescript Application crashes at start

I created a few applescript applications to automate some features in iTunes. (Namely to update podcasts, to play a playlist for a fixed period of time and to turn iTunes off after a user selected time interval.) These applications worked fine in Tiger but quit when started under Leopard. Has any body seen this problem?

What I have done so far:

  1. The scripts perform properly when run from the Script Editor.
  2. The scripts perform properly when saved as scripts and called from iTunes.
  3. Resaved the scripts as applications. The new applications still quit at startup.
  4. Saved one of the scripts as an application bundle. The application bundle executed properly at least once.
    (I have placed this bundle into its workflow and I am waiting to see if it performs properly.)

So a second question is; Why do Application Bundles work but Applications do not?

OS X 10.5.1 AppleScript 2.0 Script Editor 2.2 iTunes 7.6

Thank you for any help you can give.