Today’s Vista Woe

I have an external USB drive that I use for backups.  This morning I went to update my backup, and plugged the drive into the PC as usual.  Vista responded with this prompt:  "You need to format the disk in drive N: before you can use it."

This is my backup drive.  The drive I would depend on if my main drive failed.  Vista won't read it.

And lest you think it's some sort of hardware failure - I plugged the drive into my Mac, and even though the Mac can't write to it (it's NTFS-formatted), the Mac can see it and all the files on it.  It's all there, apparently undamaged, but Vista thinks the drive isn't even formatted.

Update:  It's a good thing I had an XP system here to try it with.  XP mounted the drive no problem.  I ran chkdsk /f on it, then brought it back over to Vista and Vista was happy with it.