Panasonic KX-TD500 System Reference Manual page 1446

3.25 OGM lost (DISA)
Error Code
Possible cause of
the malfunction
Countermeasures
Note
51xx
xx= 01 to 40 : Slot number
1) Power failure or power-off for long duration (6~7 days).
2) Defective backup battery for DISA card.
3) OGM was not recorded after the installation.
After confirming the OGM recording/
playback through the phone of
Operator 1, press the RESET button
Is there a new related error
message in the Error Log ?
Yes
None
Replace the DISA card
15-E-28
No
End