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You run the ForestPrep operation by using the setup.exe /prepareschema command in a Microsoft Windows Server 2003 domain. You do this to prepare a Windows Server 2003 Active Directory directory service forest for Microsoft Exchange Server 2007.

When you do this, you receive the following error message:

Schema update failed: An attribute with the same link identifier already exists.

CAUSE

This issue occurs when the ForestPrep operation encounters a link identifier (linkID) in the Active Directory schema that is the same as the linkID that the Exchange Server Setup program tries to import into Active Directory.

You may experience this issue when the following conditions are true:

•	A third-party program that extends the Active Directory schema is installed in the domain.
•	That third-party program uses a method to extend the schema that resembles the method that was previously documented on the Microsoft MSDN Web site.Note This previous method to extend the schema provided sample code to detect the existing linkIDs in the schema. The code then selected higher values that would not conflict with existing linkIDs.

This previous method of extending the Active Directory schema may conflict with the installation of Exchange Server 2007.

The current method to extend the schema requests a set of available linkIDs from the linkID registration database.

The current method to extend the schema includes the following attributes. These attributes may conflict with third-party programs:

•	CN=ms-Exch-ELC-Folder-Link,<SchemaContainerDN> linkID: 2054
•	CN=ms-Exch-ELC-Folder-BL,<SchemaContainerDN> linkID: 2055
•	CN=ms-Exch-Mailbox-Template-Link,<SchemaContainerDN> linkID: 2056
•	CN=ms-Exch-Mailbox-Template-BL,<SchemaContainerDN> linkID: 2057

The remaining linkIDs that the current method adds are unlikely to conflict with schema extensions that are added by third-party programs.

WORKAROUND

To work around this issue, modify the linkIDs in the PostExchange2003_schema5.ldf file to change the conflicting linkID values. To do this, follow these steps:

1.	Copy the contents of the Exchange Server 2007 CD to a folder on the local hard disk.
2.	In this folder, locate the \Setup\Data folder.
3.	Open the PostExchange2003_schema5.ldf file by using a text editor such as Notepad.
4.	Locate the following section: dn: CN=ms-Exch-ELC-Folder-Link,<SchemaContainerDN> To do this, follow these steps: a. In Notepad, click Find on the Edit menu. b. In the Find what box, type ms-Exch-ELC-Folder-Link, and then click Find Next.
5.	Under dn: CN=ms-Exch-ELC-Folder-Link,<SchemaContainerDN>, locate the following entry: linkID: 2054
6.	Replace the value of 2054 with the value of 1138.Note The Exchange Server Product Group has reserved linkIDs 1138 to 1141 for Exchange Server 2007. These linkID values do not conflict with existing or future versions of Exchange Server.
7.	Repeat steps 4 to 6 for the other linkID values. Replace 2055 with 1139, and so on.
8.	On the File menu, click Save to save the changes to the PostExchange2003_schema5.ldf file.
9.	Exit the text editor.
10.	In the folder to which you copied the contents of the Exchange Server 2007 CD, prepare the forest for Exchange Server. To do this, run the Setup.exe /prepareschema command.

MORE INFORMATION

The Exchange Server Product Group has approved these steps as a supported workaround for the issue that is described in this article. These steps do not damage Active Directory. LinkIDs 1138 to 1141 are reserved for Exchange Server 2007 and do not conflict with future Microsoft products.

Important After you import objects into the Windows Server 2003 Active Directory schema, you cannot remove them. Therefore, we recommend that you carefully consider any changes to the Active Directory schema. If you incorrectly extend the Active Directory schema, you may experience problems with Active Directory.

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APPLIES TO

•	Microsoft Exchange Server 2007 Enterprise Edition
•	Microsoft Exchange Server 2007 Standard Edition

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Microsoft Knowledge Base Article

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