1785 Drive Array Not configured, Run ADU

[CA1183979]

Hopefully a straight forward one but can someone explain the following ?

I have 2 DL380G3's :
Server A has 3 sets of Raid 1 (6x36Gb)
Server B has Raid 1 (2x36Gb) and Raid 5 (4x144Gb)

Part of our disaster recovery testing was to pretend a motherboard had failed on one of the servers so we pulled the disks (6x36Gb) and put into the other server - it booted up fine (Windows 2003 redetected a few things, rebooted and all was well)

I then tried to move just the Raid 5 (4x144Gb) from Server B into Server A (removing 4x36Gb) and it fails to boot with
1785 Drive Array Not configured, Run ADU

I'm assuming you can move all disks between like array controllers (both 5i) but you can't move some disks ?

Does the array controller write the info across all disks ? Is there a tool that can be used to tell it its new config ?

Thanks