Hi,I have at least 6 users that are now being prompted for a username and password when opening Outlook.Some other things I'ved noticed which may give some clues: (because I think they're related)Login Script - they get prompted for there username and password during the logon script.Exchange server Event log: is getting hammered with security failure audits.529, 537, 680 - examples belowThe users reported in the event log are not just the ones with above issues.Clues anyone? Kerberos or authentication issue?Event Log examples.Event 537Event Category: Logon/Logoff User: NT AUTHORITY\SYSTEMDescription:Logon Failure: Reason: An error occurred during logon User Name: *username* Domain: *domain* Logon Type: 3 Logon Process: Kerberos Authentication Package: Kerberos Workstation Name: - Status code: 0xC00002EE Substatus code: 0x0alsoEvent 537Event Category: Logon/Logoff User: NT AUTHORITY\SYSTEMLogon Failure: Reason: An error occurred during logon User Name: Domain: Logon Type: 3 Logon Process: Kerberos Authentication Package: Kerberos Workstation Name: - Status code: 0xC000006D Substatus code: 0xC0000133 Source Network Address: *IP address* Source Port: 2829alsoEvent Category: Logon/Logoff Event ID: 529User: NT AUTHORITY\SYSTEMDescription:Logon Failure: Reason: Unknown user name or bad password User Name: master Domain: Logon Type: 3 Logon Process: Advapi Authentication Package: MICROSOFT_AUTHENTICATION_PACKAGE_V1_0 Workstation Name: MELBEXCHANGE01 Caller User Name: MELBEXCHANGE01$ Caller Domain: *domain* Caller Logon ID: (0x0,0x3E7) Caller Process ID: 1400 Transited Services: - Source Network Address: - Source Port: -alsoEvent Category: Logon/Logoff Event ID: 529Description:Logon Failure: Reason: Unknown user name or bad password User Name: *username* Domain: *domain* Logon Type: 3 Logon Process: NtLmSsp Authentication Package: NTLM Workstation Name: *machine* Source Network Address: *ip* Source Port: 1165alsoEvent Category: Account Logon Event ID: 680Description:Logon attempt by: MICROSOFT_AUTHENTICATION_PACKAGE_V1_0Logon account: *username* or *username@domain.com*Source Workstation: *workstation*Error Code: 0xC0000064

Hi, First, you can see if the following KB helps. Outlook Continues to Prompt You for Logon Credentials http://support.microsoft.com/kb/312630 Then make sure the your account settings->more setting- > security tab- >always prompt for credentials is not checked. Check the logon network security and choose the negotiate authentication to test the issue again. If the issue persists, I suggest create a new Windows profile to narrow down the issue. Regarding the Kerberos Authentication, it is the default method of network authentication for services in Windows Server. The client always first use Kerberos Authentication as the authentication method, then try NTLM if Kerberos is unavailable. If the issue is confirmed as a Kerberos authentication issue, I think we may need discuss the issue in Windows Server forums. Hope this helps. Thanks, Elvis