Hello Hui,
What kind of computer are you using to control this system? Another possible cause of this error could be that the system is not fast enough to read the samples from the 6602 before they are overwritten.
See if you can reproduce the error with a single 4472 and a 6608. Then try to reproduce the error with all 4472s, but not the 6608. You might also want to try to reproduce this with a different computer. Let me know when you get a chance to continue this troubleshooting.
Regards,
Sean C.
