You are intermittently prompted for credentials or experience time-outs when you connect to Authenticated Services

To resolve the issue, use one or more of the following methods:

• Install the following hotfix, and then follow the steps that are described in the "Registry information" section. After you install this hotfix on Windows Vista, Windows Server 2008, Windows 7, or Windows Server 2008 R2, the maximumlimit of concurrent connections between a client computer and another server or a domain controller for NTLM authentication or PAC validation may be changed up to 150. This should be done on all servers that exhibit Perfmon Netlogon “semaphore time-out” indications in their Performance logs or that have the “NlpUserValidateHigher: Can't allocate Client API slot” text in their Netlogon debug logs.
• For applications and services that are using NTLM, just configure them to use Kerberos authentication instead. The methods to do that will be unique to those applications.

Note In order to decide what value to set for the MaxConcurrentApi setting in your environment refer to the Knowledge Base article below.

2688798 How to do performance tuning for NTLM authentication by using the MaxConcurrentApi setting

Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing the problem that is described in this article. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft website:

http://support.microsoft.com/contactus/?ws=support

Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Prerequisites

To apply this hotfix, your computer must be running Windows 7, Windows Server 2008 R2, Windows Vista Service Pack 2, or Windows Server 2008 Service Pack 2.

Registry information

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756 How to back up and restore the registry in Windows

After you install the hotfix, increase the Maxconcurrentapi value to a larger number on all servers that have Perfmon Netlogon "semaphore timeout" indications in their Performance logs or that have "NlpUserValidateHigher: Can't allocate Client API slot" text in their Netlogon debug logs. To do this, follow these steps:

1. Start Registry Editor.
2. Locate the following registry subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters
3. Create the following registry entry:
   
   Name: MaxConcurrentApi
   Type: REG_DWORD
   Value:Set the value to the larger number, which you tested (any number greater than the default value).
4. At a command prompt, run net stop netlogon, and then run net start netlogon.

Notes

• The maximum value that can be configured depends on the operating system version and whether a hotfix is available.
  • The maximum configurable setting in Windows Server 2003 is 10.
  • The maximum configurable setting in Windows Server 2008 (without the hotfix in this article) is 10. With the hotfix, the maximum is 150.
  • The maximum configurable setting in Windows Server 2008 R2 (without the hotfix in this article) is 10. With the hotfix, the maximum is 150.
• If you decide to increase the MaxConcurrentApivalue to greater than 10, the load and the performance of the desired setting should be tested in a nonproduction environment before you implement in production. This is recommended to make sure that increasing this value does not cause other resource bottlenecks.

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace a previously released hotfix.

File information

The English (United States) version of this hotfix installs files that have the attributes that are listed in the following tables. The dates and the times for these files are listed in Coordinated Universal Time (UTC). The dates and the times for these files on your local computer are displayed in your local time together with your current daylight saving time (DST) bias. Additionally, the dates and the times may change when you perform certain operations on the files.

• The MANIFEST files (.manifest) and the MUM files (.mum) that are installed for each environment are listed separately in the "Additional file information for Windows Vista and Windows Server 2008" section. MUM and MANIFEST files, and the associated security catalog (.cat) files, are very important to maintaining the state of the updated component. The security catalog files, for which the attributes are not listed, are signed with a Microsoft digital signature.

File information for Windows Vista and for Windows Server 2008

File information for x86-based versions of Windows Server 2008 and of Windows Vista

File information for x64-based versions of Windows Server 2008 and of Windows Vista

File information for IA-64-based versions of Windows Server 2008

File Information for Windows 7 and for Windows Server 2008 R2

Windows 7 and Windows Server 2008 R2 file information notes
Important Windows 7 hotfixes and Windows Server 2008 R2 hotfixes are included in the same packages. However, hotfixes on the Hotfix Request page are listed under both operating systems. To request the hotfix package that applies to one or to both operating systems, select the hotfix that is listed under "Windows 7/Windows Server 2008 R2" on the page. Always refer to the "Applies To" section in articles to determine the actual operating system to which each hotfix applies.

• The MANIFEST files (.manifest) and the MUM files (.mum) that are installed for each environment are listed separately in the "Additional file information for Windows Server 2008 R2 and for Windows 7" section. MUM and MANIFEST files, and the associated security catalog (.cat) files, are very important to maintaining the state of the updated component. The security catalog files, for which the attributes are not listed, are signed with a Microsoft digital signature.

For all supported x86-based versions of Windows 7

For all supported x64-based versions of Windows 7 and of Windows Server 2008 R2

For all supported IA-64-based versions of Windows Server 2008 R2