The kerberos client received a KRB_AP_ERR_MODIFIED error from the server

The article helps you to resolve the issue that the kerberos client received a KRB_AP_ERR_MODIFIED error from the server.

Applies to:   Windows Server 2003
Original KB number:   558115


During access to NLB virtual IP/NLB Virtual Name, the user may prompt to a username and password, and the following error may add to the local system event log:

Event ID: 4
Source: Kerberos
Type: Error

"The kerberos client received a KRB_AP_ERR_MODIFIED error from the server host/ This indicates that the password used to encrypt the kerberos service ticket is different than that on the target server. Commonly, this is due to identically named machine accounts in the target realm (, and the client realm. Please contact your system administrator."


During access to the IIS 6 web site that support Windows Integrated Authentication, the following issues may occur:

  1. Mismatch DNS name resolution. The issue is common in an NLB environment that uses multiple IPs or network adapters.
  2. The user doesn't have a Local NTFS access permission.
  3. The Web Site is using Application Pool with a poor permission setting.


To resolve the error issue, consider to implement the following tests:

  1. Verify that the IIS has been set up with correct NTFS settings.

    Integrated Windows Authentication (IIS 6.0)

  2. Verify that each cluster node has been set up with correct DNS settings.

  3. Verify that the node has been set up with correct Application Pool settings:

    Configuring Application Pool Identity with IIS 6.0 (IIS 6.0)

  4. Verify that internet explorer has been set up with a correct security setting.

More information

Authentication and Access Control Diagnostics 1.0 (x86)

Internet Information Services Diagnostic Tools

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