Maybe there's a problem with the MBR on your device (sdc), try testdisk and maybe it will be able to fix it on sdc? Or, sdc itself might have some physical errors, personally I've had some problems with usb flash memory (sd cards, thumbdrives) and multiple partitions.
Or maybe there's a problem with the partition backup (hbcd.iso), try
fsck.msdos -n /var/isos/hbcd.iso
and see if it likes the fat32 partition or not. (-n makes no changes, just to check)
Or First, to just get the data, directly mounting the hbcd.iso file should work if it's a good fat32 filesystem, then you could copy everything out of it without playing with sdc at all. Testdisk can copy the files out of it directly too and may work better if there's some problems with it (run testdisk hbcd.iso). Something like this should work:
mount -o loop,ro hbcd.iso [somedir]
And if mounting & testdisk can't read the filesystem then photorec (part of the testdisk package) can carve the data out of hbcd.iso, but it probably won't keep any original filenames. I think sleuthkit should have some good data carving tools, maybe even testdisk/photorec.
Don't forget the data recovery rule: MAKE A BACKUP COPY AND PLAY WITH IT FIRST!
Otherwise some small typo or a naughty program could erase everything, so backup that hbcd.iso.