McPata2002, It's very strange that the editor would work for you but not the viewer as they're the same exact sort of file: a .XAP
In IE9, could you please:
1) navigate to a view page,
2) hold the [Ctrl] key and then tap the [F5] key while holding [Ctrl]
(to try to do a hard refresh of the view page and all associated files, including the viewer app)
Another way to do this, would be to clear IE9's cache (probably called "temporary internet files"). Don't clear your cookies or history - just your cache.