I usually work with live versions of Ubuntu. I have a NAS which I use for saving files from computers. When I save files to NAS everything works ok but when I try to recover files from NAS to the computer everything goes wrong. Using Ubuntu 9.04 and 9.10 it works properly, but from 10.04 on it stops working and you can't take the files from the NAS.
My guess, based on the little information in your post, is that this is a permissions problem. If you are using NFS to access the NAS from ubuntu, permissions are managed using numeric user identifiers. The NAS tracks these, the client (your desktop) translates the numbers into user names. Most likely, between the different versions, the user name you are using got assigned a different UID. Probably, it used to be 1000, now it is 1001. (Unless running off a live CD means you are root all the time?)
As a first step to debugging, how are you accessing the NAS, and can you do an
ls -l of the problem files? (All we want is the left hand columns, not the file names)