The event was fine for a while for one of my scripts, but now keeps failing (returning false). The function sets an image control with an image of the internet. It did work when I tested it. I packed it and ran it and it didn't work in the new version. I deleted the temp files in the previous version and that one stopped downloading as well. Is there any reason why a file that I can manually access over the web, can't be downloaded?

I've done something like this recently and it has worked absolutely fine for me and a few other people.  You have to make sure you don't delete the temp file until you update the picture or destroy the window I found.  Also you may want to clear the cache before getting the image if you are accessing the same image a few times.  Finally, check that the URL being returned when you get the false is the one you are after, I do realise that this sounds like common sense but it can never hurt to triple check these things.