Error Code -36 !!! PANIC

Hi,

I have an external RAID enclosure with 2 300GB Hard drives set to RAID 1 for redundancy connected via Firewire to my Imac. There is one volume on the Raid setup formatted to Mac OS Extended (Journaled). All of a sudden I cannot write any more to the disk. When I am trying to copy a file I get:
"The finder cannot complete the operation because some data in'Filename' could not be read or written. (Error Code -36)"

I tried using disk utility to repair the disk without success:
Verifying volume “RAID Drive”
Checking HFS Plus volume.
Invalid number of allocation blocks
The volume needs to be repaired.

Error: The underlying task reported failure on exit


1 HFS volume checked
Volume needs repair

I read around about the problem and found out that I can move or copy a file to the disk using the terminal but when I try to open the file i copied using finder I get: "File error. Couldnt Open File"

This drive contains all of my Photography work, and I do have backups, but the backups I have are seperate catalogs on DVDs and it would take ages to restore all the data. Besides, the data I have on the drive is still perfectly readable (apart from the ones i copied using the terminal). I just cannot write to it!

Any ideas to how to go about repairing the disk? Are there any freeware disk utility applications?

Regards,

tonio