21ip check 100

[Duffy]

Customer getting random check 100 on vista 21ip system.
I changed out rf keypad(matched all existing settings) and showed up again couple hours after I left. I enabled rf jam detection first visit and there weren't any in history 2nd visit.
System has worked fine for over 6 years, four keypads and only 3-5 other devices drawing from aux power. Voltage reading 13.6vdc at all keypads.
Any suggestions appreciated!