Mail folder "undefined" could not be found

[gui]

Hello,

Our customer experiencing on many imap Dovecot users an error message in the OX webmail 6.18 (appears in /var/log/open-xchange/open-xchange.log.*) :

20 oct. 2010 16:10:18 com.openexchange.ajax.Mail actionGetAllMails
GRAVE: IMAP-1002 Category=8 Message=Mail folder "undefined" could not be found on server 127.0.0.1 with login <user> (user=61, context=1). exceptionID=-896783237-224153
IMAP-1002 Category=8 Message=Mail folder "undefined" could not be found on server 127.0.0.1 with login <user> (user=61, context=1). exceptionID=-896783237-224153
        at com.openexchange.imap.IMAPException.create(IMAPException.java:893)
        at com.openexchange.imap.IMAPException.create(IMAPException.java:857)
        at com.openexchange.imap.IMAPFolderWorker.setAndOpenFolder(IMAPFolderWorker.java:339)
        at com.openexchange.imap.IMAPMessageStorage.searchMessages(IMAPMessageStorage.java:383)
        at com.openexchange.mail.MailServletInterfaceImpl.getMessagesInternal(MailServletInterfaceImpl.java:1121)
        at com.openexchange.mail.MailServletInterfaceImpl.getMessages(MailServletInterfaceImpl.java:1111)
        at com.openexchange.mail.MailServletInterfaceImpl.getAllMessages(MailServletInterfaceImpl.java:598)
        at com.openexchange.ajax.Mail.actionGetAllMails(Mail.java:716)
        at com.openexchange.ajax.Mail.actionGetAllMails(Mail.java:591)
        at com.openexchange.ajax.request.MailRequest.action(MailRequest.java:115)
        at com.openexchange.ajax.Multiple.doAction(Multiple.java:293)
        at com.openexchange.ajax.Multiple.parseActionElement(Multiple.java:178)
        at com.openexchange.ajax.Multiple.doPut(Multiple.java:126)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:619)
        at com.openexchange.ajax.AJAXServlet.service(AJAXServlet.java:386)
        at com.openexchange.ajax.SessionServlet.service(SessionServlet.java:165)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
        at com.openexchange.ajp13.najp.AJPv13RequestHandlerImpl.doServletService(AJPv13RequestHandlerImpl.java:504)
        at com.openexchange.ajp13.AJPv13Request.response(AJPv13Request.java:129)
        at com.openexchange.ajp13.najp.AJPv13RequestHandlerImpl.createResponse(AJPv13RequestHandlerImpl.java:316)
        at com.openexchange.ajp13.najp.AJPv13ConnectionImpl.createResponse(AJPv13ConnectionImpl.java:207)
        at com.openexchange.ajp13.najp.AJPv13Task.call(AJPv13Task.java:346)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
        at java.util.concurrent.FutureTask.run(FutureTask.java:138)
        at com.openexchange.threadpool.internal.CustomThreadPoolExecutor$Worker.runTask(CustomThreadPoolExecutor.java:737)
        at com.openexchange.threadpool.internal.CustomThreadPoolExecutor$Worker.run(CustomThreadPoolExecutor.java:763)
        at java.lang.Thread.run(Thread.java:619)

The error message disappear when clicking on the Inbox.
I think the problem is on Dovecot side, but full debug don't give any clue for the moment.

Thanks in advance for any other clues to explore.

[Viktor Pracht]

Are there any errors shortly before that error in the server log? Are there any errors in the error console in the browser?

[gui]

No error before the previous reported, just informational messages :

INFO: Login:<user> IP:xx.xx.xx.xx AuthID:c1a8ae0914d144bdac4b8308d05abe23 Agent:Jakarta Commons-HttpClient/3.1 Client:null(null) Interface:HTTP_JSON Context:1(1,<customer>,defaultcontext) User:50(<user>) Session:1694e4d9f72047a2929fa90454dd53b5
22 oct. 2010 13:05:48 com.openexchange.login.internal.LoginPerformer logLoginRequest
INFO: Login:<user> IP:xx.xx.xx.xx AuthID:829ff1eed16a4bba80cc3cd51bd3a521 Agent:Jakarta Commons-HttpClient/3.1 Client:null(null) Interface:HTTP_JSON Context:1(1,<customer>,defaultcontext) User:50(<user>) Session:5b6556983c404e28856b144c0d3a80b2