After upgrade to Server 4.1 Calendar server can't send invitation

Anybody run into this issue? From OS X (10.10.3) calendar send invitation to Open Directory users, but recipient never receive the invitation.

Server Calendar log report thousands of error

2015-06-17 11:52:21+0800 [-] [twext.enterprise.jobqueue#error] Failed to pick a new job, 'SCHEDULE_REPLY_CANCEL_WORK'

2015-06-17 11:52:21+0800 [-] [twext.enterprise.jobqueue#error] Failed to pick a new job, 'SCHEDULE_REPLY_CANCEL_WORK'

Many thank for any suggestion.