CUP redundency group fails

[iptsupport]

Hi  , 

I  am using CUCM and CUP version 11.5 and noticed that the redendency group of the CUPS 

keep on failing . When I click the failover button it comes back to normal normal state .I logged in the RTMT and found the error attached . All the servers are in the same LAN and Vlan  . Any idea how to troubleshoot this issue ?  

[Jonathan Schulenberg]

I have seen the IM&P cluster failing repeatedly when the cluster doesn’t have a reliable NTPv4 time source. The CUCM publisher should be obtaining time from an external time source - not Windows! - and all CUCM subscribers plus the IM&P pub/sub(s) should all be getting time from the CUCM pub.

[iptsupport]

I checked the NTP and it synchronized and using proper server any other idea what can cause this problem ?