Some customers have experienced problems with the current version of the firmware in older G4 machines. Sonnet suggests downgrading the firmware to the Version 5.13, which can be found at http://www.firmtek.com/download/SeriTek1S2_513.zip
The Stardom RAIDSONIC ST3620-2S-S2 is not reliable when connected at 6Gb. It was designed for 3Gb SATA. If you connected previously using a 3Gb controller, even with 6Gb drives, the connection was 3Gb. With the 6Gb controllers and 6Gb drives, the connection is negotiated at 6Gb, but the connection is not reliable because of the older design of the Stardom chassis does not support 6Gb. The drives may not be recognized or if recognized, transfers will fail at some point.