What client OS are you running? If you are using Windows 2008 or Vista, you may want to try the solution in http://www.intel.com/support/motherboards/server/sb/CS-030717.htm.
Some other common suggestions include updating NIC driver and SS4200-E firmware. You can also try tranferring file from another system to isolate the issue.
On my desktop Windows Vista Home w SP2, latest network driver and nas also have latest firmware. I have tryed the fixes you recommend and slow transfer persist, unfortunately I dont have another 1G network capable PC on my network to check if its an isolate issue.
Edit: Problem solved: I just reinstalled windows and now is working perfect! Now I can copy files at ~70-90MB/s
This topic can be closed