Asus Z9PA-U8 - Manual (Page 40)

2-20 Chapter 2: Hardware information
4. CATT Error LED (CATTERR_LED1)
Indicates that the system has experienced a fatal or catastrophic error and
cannot continue to operate.
3. DIMM warning LED (ERR_DIMM)
The DIMM warning LEDs light up to indicate an impending failure of the
corresponding DIMMs.
The warning LEDs function only when you install the ASUS ASMB6.