dosfsck

$ sudo dosfsck -a /dev/sdb1
dosfsck 3.0.7, 24 Dec 2009, FAT32, LFN
There are differences between boot sector and its backup.
Differences: (offset:original/backup)
  28:3f/00
  Not automatically fixing this.
Root contains directory ".". Dropping it.
Root contains directory "..". Dropping it.
Unable to create unique name