mounting msdos partitions buggy?

[Greg J.]

 > Have you verified that your FAT partition is not corrupted by running
 > fsck_msdos against it?

fsck_msdosfs doesn't even seem to recognize it.. I know there's nothing 
wrong with the partition.

I even did a clean install of FreeBSD & Win2k... and moved the fat32 
partition to another drive. But I still get the same behaviour.

localhost# fsck_msdosfs /dev/ad1s5
** /dev/ad1s5
backup doesn't compare to primary bootblock
localhost# mount -t msdos /dev/ad1s5 /msdos
localhost# fsck_msdosfs /msdos
** /msdos (NO WRITE)
Invalid signature in boot block: ffff