Issue with data monitoring

Hi all

I face a issue related to data monitoring. as described this message:

Monitoring process failed, please check the logs. Time: 2016-10-14T00:00:00.717Z. System: Staging Message: null Cause:

And that is errors in the log:

* INFO 2016-10-14 00:00:00,002 Starting scheduled monitoring task (DefaultValidationRuleService. java [taskScheduler-6])

* INFO 2016-10-14 00:00:00,658 Scheduled monitoring run sources: 3716, periods: 4, rules:63, last run: Tue Aug 30 03:38:36 UTC 2016 (DefaultValidationRuleService. java [taskScheduler-6])

* INFO 2016-10-14 00:00:00,739 ‘system-process’ create org.hisp.dhis.message. MessageConversation, name: Monitoring process failed, uid: nMoxsKYQEnO ( [taskScheduler-6])

at org.hisp.dhis.validation.

I start removing groups/rules one by one (on staging) to see if the error disappears, but nothing.

DHIS2 version used : 2.20 build : 20033 and 2.24 build : f25d31a

Anyone has experienced this issue.