I was having this problem too with my 2010 Honda Insight EX, before I googled this and found a blog post with a solution to this problem. Try this...
* Download the HP USB Disk Storage Format Tool from this site:
HP USB Disk Storage Format Tool | Peripherals Download | PC World
* Install it on your computer.
* Reformat the USB drive using this software. Please back up anything you have the drive before doing this.
* Copy your music files to the newly formatted USB drive.
This should work and the USB interface should recognize the drive without any errors. I think this is an issue with the newer drives that are used with Microsoft Vista. Let me know if this works.