I might be a long way from the answer, but if I can suggest, repair permissions, run whatever osx utilities you have (preferably 3rd party if you have them such as Norton or/& any others; eg: DiskWarrior & TechTool Pro), restart your computer & try again. There's certain issues in OSX that are not made clear to us (such as could've been fixed easily in os9 & before), but I believe 'some' of these principles are probably the same. But how to fix them is not so apparent! (It could be anything from corrupt prefs to recognition of file types.) Sometimes it takes drastic measures to answer these issues such as reinstalling some apps. Has Expander given you issues with anything else before? It's clashing with other apps for some reason!