Readynas Duo crashes (or hangs) on big filecopy

My Readynas DUO crashes consistently while copying a large file. The first time I copied a video file (300MB) from one place on the NAS to another (on the NAS) by means of a NFS share and Nautulus on my Ubuntu PC. To eliminate nfs I copied the file on the readynas command line from the same origin to the same destination. During the copy I loose all connections from my PC to the NAS, so it is not clear if the system crashes or hangs in some way. The readynas responds correctly on the power down button on the front of the DUO. I cannot ping the NAS from anywhere so the network is completely lost. The only thing to do is power down with the button.

In the messages file the following line is present:

May 28 20:32:38 netgear kernel: rxS1(00ca0000),rxS0(008005ee)

I have seen the same messages several times in the messages file: sometimes it occurs just before the system hangs but not always.
Once I have seen this message appear (in tail -f /var/log/messages) immediately followed by the hang (or crash). At that time there was hardly any network activity so it seems clear to me that the filecopy just started before that is the cause of the hang.

My Smart data of the two disks show the following information:

Model: 	SAMSUNG HD103UJ
Serial: 	S13PJ9AS705549
Firmware: 	1AA01118

SMART Attribute
	
Raw Read Error Rate	0
Spin Up Time	9690
Start Stop Count	12119
Reallocated Sector Count	0
Seek Error Rate	0
Seek Time Performance	0
Power On Hours	39613
Spin Retry Count	0
Calibration Retry Count	0
Power Cycle Count	25
Read Soft Error Rate	0
Runtime Bad Block	0
End-to-End Error	0
Reported Uncorrect	0
Command Timeout	0
Airflow Temperature Cel	34
Temperature Celsius	36
Hardware ECC Recovered	43898143
Reallocated Event Count	0
Current Pending Sector	0
Offline Uncorrectable	0
UDMA CRC Error Count	0
Multi Zone Error Rate	0
Soft Read Error Rate	0
	
ATA Error Count	0

Extended Attribute
	
Hot-add events	0
Hot-remove events	0
Lp stat events	0
Power glitches	0
Hard disk resets	0
Retries	0
Repaired sectors	0

and the following for the second disk:

Model: 	SAMSUNG HD103UJ
Serial: 	S13PJ90S761084
Firmware: 	1AA01118

SMART Attribute
	
Raw Read Error Rate	34
Spin Up Time	9950
Start Stop Count	12205
Reallocated Sector Count	0
Seek Error Rate	0
Seek Time Performance	0
Power On Hours	39603
Spin Retry Count	0
Calibration Retry Count	0
Power Cycle Count	23
Read Soft Error Rate	0
Runtime Bad Block	0
End-to-End Error	0
Reported Uncorrect	0
Command Timeout	0
Airflow Temperature Cel	33
Temperature Celsius	35
Hardware ECC Recovered	19397
Reallocated Event Count	0
Current Pending Sector	0
Offline Uncorrectable	0
UDMA CRC Error Count	0
Multi Zone Error Rate	1
Soft Read Error Rate	0
	
ATA Error Count	0

Extended Attribute
	
Hot-add events	0
Hot-remove events	0
Lp stat events	0
Power glitches	0
Hard disk resets	0
Retries	0
Repaired sectors	0

The first disk has a high Hardware ECC Recovered (always has been high).
The second disk seems to have a Raw Read Error Rate where it was 0 (I think).

Otherwise I don't see any strange things in the log files.

Does anybody know what could be the reason of my problems?
In other posts this behavour is also described but I think I can rule out any network related problem. To me it seems a disk problem.
What can I do to confirm and remedy this problem? After a resync and deleting of some files I can not initiate this problem anymore.