I managed to solve the problem!

There is a bios setting on my motherboard (X7DWN+) that sets the 'max payload size'
for PCI-Express devices. This setting was default on 256, when I had set this to 128 the problem was gone.

Areca support (as good as the cards are ) has confirmed that the Areca raidcontrollers use a default payload setting of 128.

Replication works fine now!