I got the same error E22 after using my LS-XH2.0TL for over a year. Since the product is already out of warranty, I decided to find out what went wrong. What surprised me is that it turned out to be software error and the problem can be fixed. Here is what I did:
1) Open the case and remove the SATA drive and put it into my PC that supports the SATA. (*)
2) Burn a Linux system rescue CD. Here is the URL: http://www.sysresccd.org/Main_Page Because the file system on the drive is XFS, you need to boot into a Linux system to see or fix the file system.
3) Once I booted into rescue CD on my PC, I tried to mount the file system on that drive. The device is recognized by the Linux as /dev/sda (that's the only drive I put in my PC for this rescue). Using gparted, it shows that /dev/sda has 6 partitions, the main data partition is the largest, and it is /dev/sda5.
4) I tried to mount /dev/sda5, and got the error message "Structure needs cleaning". This is exactly the reason why the LinkStation can't mount the file system in my case.
5) I then followed the instruction on http://xfs.org/index.php/XFS_FAQ#Q:_I_see_applications_returning_error_990_or_.22Structure_needs_cleaning.22.2C_what_is_wrong.3F
First using xfs_check to confirm there is problem for the file system, and then used xfs_repair to fix the device (with -L option).
6) Then I was able to mount /dev/sda5 on my PC.
7) After that, I put the drive back to the LinkStation device, everything is back to work.
(*) To open the case, you need to remove labels at the buttom, and insert flat head screw drivers into the two small openings and insert pins on the top the help open the case.
I think I may get this problem again in the future when the XFS meta data is out of sync again...
Hope it helps to those whose products are out of warranty and need to rescue data.
Ji