I've found a strange bug in Internet Explorer 7 (haven't tried IE6 or IE8, might be the same problem there).
I've searched everywhere and all I have found is a post about the exact same problem:
You can read about the problem above, but in short:
1. start a couple of loaders (for example to load images)
2. close the tab while loading the images
3. now you can't go to that page again (not even a different page with the same swf)
I have tried to use stopandunload on all loaders and to remove the swf object. Both solution works, but only if I wait a couple of seconds. But those solutions won't work because the user should be able to close the window and then open it.
Dont work with swfobject either.