Error message when you create network printers on a Remote Desktop Session Host server that is running Windows Server 2008 R2: "ERROR_UNKNOWN_PORT"

Applies to: Windows Server 2008 R2


Consider the following scenario:

  • You install the Remote Desktop Services role on a computer that is running Windows Server 2008 R2.
  • Multiple users use the remote desktop connection (RDC) utility to connect to the computer.
  • Network printers are created for the user automatically when the user is logged in.
In this scenario, some network printers are not created, and you receive the following error message on the computer:


The issue occurs because of a race condition in the Print Spooler service. When the Print Spooler service adds a network printer, it does the following:
  1. The service adds a port.
  2. The service initializes the printer settings.
  3. The service adds the printer to the port.
There is a small interval when a new port has no associated printer. When this race condition occurs, a thread deletes all the orphan ports during this interval. Therefore, this new port is deleted, and you receive the error message.


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 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: 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.


To apply this hotfix, your computer must be running Windows Server 2008 R2. Additionally, you must install the Remote Desktop Services role on the computer.

Registry information

To use the hotfix in this package, you do not have to make any changes to the registry.

Restart requirement

You may have to restart the computer after you apply this hotfix.

Note To avoid restarting the computer, you can stop the Print Spooler service before you install the 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.
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 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 that each hotfix applies to.
  • 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" section. MUM and MANIFEST files, and the associated security catalog (.cat) files, are extremely important to maintain the state of the updated components. The security catalog files, for which the attributes are not listed, are signed with a Microsoft digital signature.
For all supported x64-based versions of Windows Server 2008 R2
File nameFile versionFile sizeDateTimePlatform


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates

Additional file information

Additional file information for Windows Server 2008 R2

Additional files for all supported x64-based versions of Windows Server 2008 R2
File nameAmd64_8dafee3ac7ae3e5be0d888f2ecc46be3_31bf3856ad364e35_6.1.7600.20798_none_a9e4ae4582d667eb.manifest
File versionNot Applicable
File size722
Date (UTC)14-Sep-2010
Time (UTC)00:02
PlatformNot Applicable
File nameAmd64_a9c5b9d804d019524379677ca38f230d_31bf3856ad364e35_6.1.7600.20798_none_997104ab82717016.manifest
File versionNot Applicable
File size720
Date (UTC)14-Sep-2010
Time (UTC)00:02
PlatformNot Applicable
File nameAmd64_microsoft-windows-p..ooler-core-localspl_31bf3856ad364e35_6.1.7600.20798_none_8c922311c5821eb7.manifest
File versionNot Applicable
File size4,845
Date (UTC)14-Sep-2010
Time (UTC)00:10
PlatformNot Applicable
File nameUpdate.mum
File versionNot Applicable
File size2,099
Date (UTC)14-Sep-2010
Time (UTC)00:02
PlatformNot Applicable
File nameX86_microsoft-windows-p..ooler-core-localspl_31bf3856ad364e35_6.1.7600.20798_none_3073878e0d24ad81.manifest
File versionNot Applicable
File size4,844
Date (UTC)14-Sep-2010
Time (UTC)00:10
PlatformNot Applicable