I've noticed this since I've updated to Froyo (many weeks ago) but I don't know if it's related to Froyo or just some random coincidence. Whenever I update an app that's stored on my SD card I get the "Failed to install application" error. It's easy to fix just move the app to the phone, but it's kind of a pain in the backside. Is there an easier fix? Or should I just keep all apps on the phone and use the SD for photos and music or something? I have a non-rooted HTC Incredible.