"man" says: dosfslabel - set or get MS-DOS filesystem label
Are the partitions ext3 or 4, NTFS, FAT32 or ??
In linux and ext filesystems, the labels are NOT "C:", "D:", etc., as in windows, they're short strings like "MINT14" or "BOOT". The ":" might be a problem...?
Try booting from the Mint install disk and (re)setting the labels with gparted.
Mint 17.1/fluxbox/pulse-less - Debian 8/fluxbox/pulse-less - Ubuntu 15.04/fluxbox/pulse-less
Please edit your original post title to include [SOLVED] if/when it is solved!