Finder crashes/closes when copying files to NAS OS X 10.8.2 Latest series MBP 13"

I am experiencing a problem where Finder crashes, or rather closes without notice when I move large folders into a NAS folder. (WEstern Digital Black Armor 6TB NAS drive, which is accessible just fine from the mac). 

doing the same thing from the terminal using the "mv" command works perfectly. It's just Finder that makes it impossible to do it. 6 out of 10 copies will fail, leaving partial folders copies to the target.

Why is this happening? Is there a way to overcome it?
You're experiencing a Samba limitation on the Mac side.  mv works because it's not using Samba.  You have two options: connect to your NAS using AFP (or something else) instead, or update your Samba configuration.

Check your log /var/log/samba/log.smbd for messages containing strings like "This can happen when using 64 bit lock offsets on 32 bit NFS mounted file systems."  If you have that error message, then edit the file /etc/smb.conf to contain these lines:

; Site-specific parameters can be added below this comment.
[Your NAS NAME]
strict locking = no ; END required configuration.