I have a mongoDB cluster of 3 replication sets

Getting this error

id_ObjectId('54f9ed416aad853b66d0c21f')", configdb: "172.31.12.107:27019,172.31.12.93:27019,172.31.12.43:27019" } result: { ok: 0.0, errmsg: "Error locking distributed lock for split. :: caused by :: 13651 error checking clock skew of cluster 172.31.12.107:27019,172.31.12.93:27019,172.31.12..

Ntp time on these servers are all synced.

output date of all servers

mongo-s3:
Tue Mar 10 18:47:41 IST 2015
mongo-s2:
Tue Mar 10 18:47:41 IST 2015
mongo-rt1:
Tue Mar 10 18:47:41 IST 2015
mongo-p3:
Tue Mar 10 18:47:41 IST 2015
mongo-s1:
Tue Mar 10 18:47:41 IST 2015
mongo-p1:
Tue Mar 10 18:47:41 IST 2015
mongo-p2:
Tue Mar 10 18:47:41 IST 2015

I restarted the cluster keeping ntp up2date , but still same error.
Please may I know what could be the problem ?