I ran into the same issue, and believe it's the HTC Connection Manager trying to install on the computer. I've noticed this ever since upgrading to 2.2. If you plug it into a Windows PC, a pop-up will ask if you want to install it.
Unfortunately, I also have no clue how to fix it.
EDIT: Don't worry though. You can hit ignore, mount the disk, and it should function properly...
I just tried it. I can confirm that this works. But what will happen or not happen when connecting to my PC. Will I be missing something?
This works the same for both Mac and Windows. On the Mac it is more annoying because it shows up as a "drive error". On Windows you will only get a 3rd drive (Verizon). As far as I know you don't need it even if you use Verizon's syncing software (for Windows). Once you follow the instructions above, the drive wont' show up on either Mac or Windows.