Event ID - 9021

Event Id9021
DescriptionMicrosoft Exchange System Attendant has generated new security keys for Exchange server -server_name- . Any passwords required by this server must be re-entered using the Exchange System Management snapin
Event InformationAfter drive C fails on a node of a cluster that hosts Exchange 2000 and the drive is restored (even from an image), the Exchange 2000 system attendant may not start when you fail over the virtual server to that node.
The following warning and error messages are logged in the Application event log(9021, 9022..etc).
Task Scheduler may also stop responding, and you may receive the following error message:
AT - system cannot find the drive specified
Task Scheduler - 0x8009000f

CAUSE: This problem may occur if the Exchange 2000 system attendant cannot read the encryption private keys in the Rsa\Machinekeys folder on the node. This can occur for any of the following reasons: The public key in the directory is corrupted (either intentionally or accidentally). The Crypto container that contains the private key is corrupted. Mad.exe (the system attendant process) does not have access to (permission for) the Crypto container.
RESOLUTION: To resolve this problem:
Locate the following folder:
drive:\Documents and Settings\All Users\Application Data\Microsoft\Crypto\RSA\Machinekeys
Take ownership of the key files and grant permission to the account that has Exchange Full Administrator permissions and to the Administrators group. -or-

Re-create the keys:
Locate any keys with the following name and entry:
07a4f4a06b8bf781dcc2ed16529b8a04_b7f437dd-1ae0-4382-a8cd-dec434287809 EXPWMGMT-bba7bd6d100e40ed9a62b6c8f3129089 RSA1H

Rename this key, and then fail over Exchange 2000 to the node. The system attendant should start without generating any errors and create a new key.
For Task Scheduler, the key file is different. Locate the following key:
Application Data\Microsoft\Crypto\RSA\S-1-5-18\d42cc0c3858a58db2db376582

Rename this key, and then create a new task to re-create the key. After you do so, Task Scheduler works.
Reference Links Cluster Machine Keys Prevent the System Attendant from Starting After Drive C on a Node Fails

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