Scheduled DataSource import failed

Error occurs when polling from external POP account. Errors are random be it the timing or the mailbox itself. The mailboxes do exist. Anyone has any ideas?

2010-04-15 15:12:42,703 WARN [ScheduledTask-6] [mid=66;] datasource - Scheduled DataSource import failed.
com.zimbra.cs.mailbox.MailServiceException: no such mailbox: 66
ExceptionId:ScheduledTask-6:1271315562703:c3e13e46d0de21df
Code:mail.NO_SUCH_MBOX Arg:(mboxId, IID, "66")
at com.zimbra.cs.mailbox.MailServiceException.NO_SUCH _MBOX(MailServiceException.java:148)
at com.zimbra.cs.mailbox.MailboxManager.getMailboxByI d(MailboxManager.java:393)
at com.zimbra.cs.mailbox.MailboxManager.getMailboxByI d(MailboxManager.java:328)
at com.zimbra.cs.datasource.DataSourceTask.call(DataS ourceTask.java:70)
at com.zimbra.cs.datasource.DataSourceTask.call(DataS ourceTask.java:30)
at com.zimbra.common.util.TaskScheduler$TaskRunner.ca ll(TaskScheduler.java:98)
at java.util.concurrent.FutureTask$Sync.innerRun(Futu reTask.java:269)
at java.util.concurrent.FutureTask.run(FutureTask.jav a:123)
at java.util.concurrent.ScheduledThreadPoolExecutor$S cheduledFutureTask.access$301(ScheduledThreadPoolE xecutor.java:65)
at java.util.concurrent.ScheduledThreadPoolExecutor$S cheduledFutureTask.run(ScheduledThreadPoolExecutor .java:172)
at java.util.concurrent.ThreadPoolExecutor$Worker.run Task(ThreadPoolExecutor.java:651)
at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:676)
at java.lang.Thread.run(Thread.java:595)