Hi i got the same / similar problem using some builds of XBMC on my pi.
I ended up in reformating everything as soon as I run into this problem.
Until recently ..
As i tried to image my xbmc XD card (8GB) using dd (e.g. dd if=/dev/sdd of=image.dd) i run into the same effect after restoring from a Delking 8 GB SD (which i took out of my Canon EOS) to a more "stable" Samsung 8GB SD (mb-ss8a).
I got this unable to mount unknown-block(179,3) error ...
So by using two different SD cards one easily can see that 8GB are not always 8 GB -- there are some block more on the Delking than on the Samsung -> resulting in this error.
I took the defective Samsung card to my notebook mounting it resulting in some error massages in dmesg ..
to fix this problem I checked the filesystem
fsck.ext4 /dev/mmcblk0p3
answering yes to start a fix on a not fitting file system
resize2fs /dev/mmcblk0p7 7300M
Guessing the FS to 7.3GB
Insert the SD into you Pi and try
It worked for me on some cards -> maybe the error is the same on single cards and different cards as the systems is "loosing" blocks in SD .. leading to "corruption"..
good luck
chewie