Dear all,
After rebuild in ubuntu, same problem occurs. But then I recheck the settings once again, and found it was a silly mistake.
The USB buffer in libusb was set to 16Mb only. When I first set the usb buffer to 200, I must have simply cat it once from the terminal and forgot to update the rule file /etc/udev/rules.d/ folder.
So when I reboot the Pi, the system the buffer is set back to 16. That was what caused the problem. After I added the buffer settings in the asi rule file, the problem is gone.. and now everything is good.
Thanks for everyone's help on this.
Stephen