I have two users who are trying to use the extenal IMAP feature and report that they keep on getting the following error:

A network service error has occurred.
msg: system failure: A370 NO Invalid mailbox name
code: service.FAILURE
method: ZmCsfeCommand.prototype.invoke
detail: soap:Receiver

I can't reproduce it myself with the 3 or 4 external imap servers I've tried, has anyone else seen this? I do get matching errors in my logs:

2008-01-10 14:23:33,159 WARN [btpool0-343] [name=kevina@zt2.rutgers.edu;mid=66;
ip=172.16.44.228;ua=ZimbraWebClient - FF2.0 (Linux)/5.0.0_GA_1869.UBUNTU6;ds=RUL
ink;] datasource - Import failed
com.zimbra.common.service.ServiceException: system failure: A370 NO Invalid mail
box name
Code:service.FAILURE
at com.zimbra.common.service.ServiceException.FAILURE (ServiceException.j
ava:183)
at com.zimbra.cs.datasource.ImapImport.importData(Ima pImport.java:337)
at com.zimbra.cs.datasource.DataSourceManager.importD ata(DataSourceManag
er.java:149)
at com.zimbra.cs.service.mail.ImportData.handle(Impor tData.java:62)
at com.zimbra.soap.SoapEngine.dispatchRequest(SoapEng ine.java:347)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:213)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:118)
at com.zimbra.soap.SoapServlet.doPost(SoapServlet.jav a:272)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:727)
at com.zimbra.cs.servlet.ZimbraServlet.service(Zimbra Servlet.java:174)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:820)
at org.mortbay.jetty.servlet.ServletHolder.handle(Ser vletHolder.java:487
)
at org.mortbay.jetty.servlet.ServletHandler$CachedCha in.doFilter(Servlet
Handler.java:1093)
at org.mortbay.servlet.UserAgentFilter.doFilter(UserA gentFilter.java:81)
at org.mortbay.servlet.GzipFilter.doFilter(GzipFilter .java:132)
at org.mortbay.jetty.servlet.ServletHandler$CachedCha in.doFilter(Servlet
Handler.java:1084)
at org.mortbay.jetty.servlet.ServletHandler.handle(Se rvletHandler.java:3
60)
at org.mortbay.jetty.security.SecurityHandler.handle( SecurityHandler.jav
a:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(Se ssionHandler.java:1
81)
at org.mortbay.jetty.handler.ContextHandler.handle(Co ntextHandler.java:7
12)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebA ppContext.java:405)
at org.mortbay.jetty.handler.ContextHandlerCollection .handle(ContextHand
lerCollection.java:211)
at org.mortbay.jetty.handler.HandlerCollection.handle (HandlerCollection.
java:114)
at org.mortbay.jetty.handler.HandlerWrapper.handle(Ha ndlerWrapper.java:1
39)
at org.mortbay.jetty.handler.RewriteHandler.handle(Re writeHandler.java:1
76)
at org.mortbay.jetty.handler.HandlerWrapper.handle(Ha ndlerWrapper.java:1
39)
at org.mortbay.jetty.Server.handle(Server.java:313)
at org.mortbay.jetty.HttpConnection.handleRequest(Htt pConnection.java:50
6)
at org.mortbay.jetty.HttpConnection$RequestHandler.co ntent(HttpConnectio
n.java:844)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser. java:644)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpPa rser.java:205)
at org.mortbay.jetty.HttpConnection.handle(HttpConnec tion.java:381)
at org.mortbay.io.nio.SelectChannelEndPoint.run(Selec tChannelEndPoint.ja
va:396)
at org.mortbay.thread.BoundedThreadPool$PoolThread.ru n(BoundedThreadPool
.java:442)
Caused by: javax.mail.MessagingException: A370 NO Invalid mailbox name;
nested exception is:
com.sun.mail.iap.CommandFailedException: A370 NO Invalid mailbox name
at com.sun.mail.imap.IMAPFolder.getUIDValidity(IMAPFo lder.java:1730)
at com.zimbra.cs.datasource.ImapImport.importData(Ima pImport.java:311)
... 32 more
Caused by: com.sun.mail.iap.CommandFailedException: A370 NO Invalid mailbox name
at com.sun.mail.iap.Protocol.handleResult(Protocol.ja va:328)
at com.sun.mail.imap.protocol.IMAPProtocol.status(IMA PProtocol.java:722)
at com.sun.mail.imap.IMAPFolder.getUIDValidity(IMAPFo lder.java:1722)
... 33 more