The MB561 does not have a built in RAID chipset. As for the RAID array, how was the RAID array created? Was the array made with Mac OS or a third party software? Since the MB561 is connected to USB, if a drive is changed to try to fix the RAID array, all the drives would disconnect because the USB connection would refresh itself. It is possible to follow the instructions to replacing a disk with the RAID software?
Which Mac OS version you are running? If you are running Mac OS 10.11 or higher, Mac OS raid functions might not work properly from older versions. One other thing to test if the unit itself is defective is to check if it can read hard drives that are not part of the RAID array.
Please follow up on these questions so we have a better idea regarding your setup.