日志：unable to switch back to queue directory

hrh101

我的系统 qmail+mysql+vpopmail:
在日志中总是有这行，好像每10秒一次，请问这是为何?

Mar 10 14:24:39 QmailServer splogger: 1078899879.423908 tcpserver: status: 1/100
Mar 10 14:24:39 QmailServer splogger: 1078899879.424399 tcpserver: pid 14885 from 192.168.54.231
Mar 10 14:24:39 QmailServer splogger: 1078899879.424529 tcpserver: ok 14885 ladder.cn:192.168.200.10:110 :192.168.54.231::2878
Mar 10 14:24:39 QmailServer splogger: 1078899879.658218 tcpserver: end 14885 status 256
Mar 10 14:24:39 QmailServer splogger: 1078899879.658337 tcpserver: status: 0/100
Mar 10 14:24:42 QmailServer qmail: 1078899882.185347 alert: unable to switch back to queue directory; HELP! sleeping...
Mar 10 14:24:52 QmailServer qmail: 1078899892.195360 alert: unable to switch back to queue directory; HELP! sleeping...
Mar 10 14:25:02 QmailServer qmail: 1078899902.205346 alert: unable to switch back to queue directory; HELP! sleeping...
Mar 10 14:25:12 QmailServer qmail: 1078899912.215376 alert: unable to switch back to queue directory; HELP! sleeping...
Mar 10 14:25:22 QmailServer qmail: 1078899922.225352 alert: unable to switch back to queue directory; HELP! sleeping...
Mar 10 14:25:32 QmailServer qmail: 1078899932.235396 alert: unable to switch back to queue directory; HELP! sleeping...
Mar 10 14:25:42 QmailServer qmail: 1078899942.245351 alert: unable to switch back to queue directory; HELP! sleeping...