In Registry Editor, locate the following key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Search 

Important:
As a cautionary measure, back up the registry keys in case any errors occur while deleting the registry keys. To back up the Search registry key branch:

1. In the console tree, click Search.
   
2. On the File menu, click Export.
   
3. In Export Registry File, under Export range, click Selected branch, and make sure that HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Search appears in the corresponding text box.
   
4. Select a location to save the file.
   
5. Name the file, and then click Save.
   

In Registry Editor, in the console tree, delete the following registry keys (where <ServerName> is the name of the server running Exchange):

To delete a key, right-click the key, click Delete, and then click Yes (as illustrated in the figure below). HKEY_LOCAL_MACHINE\Software\Microsoft\Search\Install

• HKEY_LOCAL_MACHINE\Software\Microsoft\Search\1.0\Applications\ExchangeServer_<ServerName>
  
• HKEY_LOCAL_MACHINE\Software\Microsoft\Search\1.0\CatalogNames\ExchangeServer_<ServerName>
  
• HKEY_LOCAL_MACHINE\Software\Microsoft\Search\1.0\Databases\ExchangeServer_<ServerName>
  
• HKEY_LOCAL_MACHINE\Software\Microsoft\Search\1.0\Gather\ExchangeServer_<ServerName>
  
• HKEY_LOCAL_MACHINE\Software\Microsoft\Search\1.0\Gathering Manager\Applications\ExchangeServer_<ServerName>
  
• HKEY_LOCAL_MACHINE\Software\Microsoft\Search\1.0\Indexer\ExchangeServer_<ServerName>
  

Deleting the Microsoft Search registry keys

Close Registry Editor.

Run Exchange Setup in Disaster Recovery mode. At a command prompt, type <drive>:\setup\i386\setup.exe /disasterrecovery where <drive> is the location of your Exchange CD.

On the Component Selection page of the Exchange Installation Wizard, under Action, Disaster Recovery is automatically selected for all installed components. To ensure that the Microsoft Search files are correctly reinstalled, under Component Name, set Microsoft Exchange to None, and then reset Microsoft Exchange back to Disaster Recovery.

Note:
Running Setup in Disaster Recovery mode installs the required Microsoft Search files to your computer.

Running Exchange Setup in Disaster Recovery mode

Click Next to continue with the installation process.

Note:

During Setup, Microsoft Search files are updated. During this time, the Confirm File Replace dialog box might appear. The dialog box prompts you to specify whether you want to overwrite certain files on your computer that are newer than the files being copied from the Exchange Setup CD. Because you are trying to repair any Microsoft Search files, you should overwrite these files. However, you can retrieve the newer versions of these overwritten when you install Exchange service packs or hotfixes.

Apply any Exchange service packs or hotfixes that were previously running on the server. To prevent the Setup program from mounting the databases after installation, you must install service packs and software updates in Disaster Recovery mode.

If you have to restore any Exchange database backups as part of this repair, restore your Exchange databases now.

Note:
For information about how to restore Exchange databases, see Restoring Exchange Mailbox or Public Folder Stores.

Restart the computer, and then make sure that the Exchange databases are mounted.

Re-create full-text indexes. For information about how to re-create full-text indexes, see How to Re-Create Full-Text Indexes.