Hello, the proxying doesn't work on my Mac (SL) and PC (WINXP).

On the PC I got this message:
com.zimbra.common.service.ServiceException: error while proxying request to target server: HTTP/1.0 407 Proxy Authentication Required
ExceptionId:sync-mbox-mail@xxxxx.de:1270797427312:46e7d19c06a4ab64
Code:service.PROXY_ERROR Argurl, STR, "https://mail.efm.de/service/soap/SyncRequest")
at com.zimbra.common.service.ServiceException.PROXY_E RROR(ServiceException.java:309)
at com.zimbra.common.soap.SoapHttpTransport.invoke(So apHttpTransport.java:240)
at com.zimbra.common.soap.SoapHttpTransport.invoke(So apHttpTransport.java:162)
at com.zimbra.common.soap.SoapTransport.invoke(SoapTr ansport.java:356)
at com.zimbra.common.soap.SoapTransport.invokeWithout Session(SoapTransport.java:342)
at com.zimbra.cs.mailbox.ZcsMailbox.sendRequest(ZcsMa ilbox.java:535)
at com.zimbra.cs.mailbox.ZcsMailbox.sendRequest(ZcsMa ilbox.java:499)
at com.zimbra.cs.mailbox.ZcsMailbox.sendRequest(ZcsMa ilbox.java:495)
at com.zimbra.cs.mailbox.ZcsMailbox.sendRequest(ZcsMa ilbox.java:491)
at com.zimbra.cs.mailbox.ZcsMailbox.sendRequest(ZcsMa ilbox.java:487)
at com.zimbra.cs.mailbox.DeltaSync.sync(DeltaSync.jav a:85)
at com.zimbra.cs.mailbox.DeltaSync.sync(DeltaSync.jav a:73)
at com.zimbra.cs.mailbox.MailboxSync.sync(MailboxSync .java:172)
at com.zimbra.cs.mailbox.ZcsMailbox.sync(ZcsMailbox.j ava:109)
at com.zimbra.cs.mailbox.ZcsMailbox.syncOnTimer(ZcsMa ilbox.java:90)
at com.zimbra.cs.mailbox.SyncMailbox$1.run(SyncMailbo x.java:255)
at java.util.TimerThread.mainLoop(Unknown Source)
at java.util.TimerThread.run(Unknown Source)

I think on the Mac is the same problem...no connection.
If I check for ZD Updates, I get a dialog Box for authentification and the updatecheck works fine.

greetings