ReadyNas 104 behaves strangely after adding disks

Hi,

I have been using th unit with two 2GB disks for a long time, and ran into a problem when adding two more drives now (WD 4TB RED). First the system did a resync over 30 hours with one of the drives (the other being grey), apparently succesfully. At the end however, the system froze, displaying error message "page_address+8" on the LED display, while the unit became unaccessible (admin interface and shares as well). After a few hours of inactivity, I restarted, the system started resync again, this time shares remaining unaccessible, the admin interface showing as below: 

The resyinc is still going on, with the following warnings coming up continually:

Can someone advise what is going on? I saw some similar threads, but not sure what is happening or what am I supposed to do with it.

Thanks, A.