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 ArgmboxId, 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)