I'm pretty certain it's my kindle. I put an Amazon supplied .azw file (the dictionary) and a Kindle Preview converted mobi onto the KF, they of course didn't show up, but then I navigated to them with File Expert, did an Open with using Kindle Reader app, and it said "Invalid item: Please remove the item from your device and go to Archived Items and download again" for both files.
The Kindle Reader app should DEFINITELY be able to open those files. And of course since it's a Kindle sysem app, I can't uninstall and reinstall it
