Whilst setting up Sharepoint 2013 on Windows server 2012 R2, we need the IIS Admin Service running on the server. But sometimes service stopped running and raised the error says "Could not start the IIS Admin Service - error code 2146893818".

Another applications having dependencies on IIS may raise the error that IIS is not installed even it is installed on the machine. This error occurs when IIS Admin Service is not running.

For environment : IIS 6, Windows Server 2012 R2

The reason behind this error is the corrupted Machine Key files. IIS depends upon these keys for encryption decryption of metabase keys and we need to make sure that Machine Key folder has full control permissions for both ADMIN and SYSTEM. If the full control permissions are not set, IISADMIN won't be able to read the configuration from the metabase without this key and it will fail to start.

These files you can find on location: "C:\Documents and Settings\All Users\Application Data\Microsoft\Crypto\RSA\MachineKeys"

Machinekey starting with C23 may have multiple instances. We need to make sure this also have the full controls permissions for both ADMIN and SYSTEM.

Solutions:
1) The Best way to solve the problem is to restore the Machinekey starting with C23 system state backup.
2) Another solution is the re-installation of IIS, it will also fix the issue.
3) Un-install and then re-install just the "IIS 6 Metabase Compatibility" Role Service also works.

Hope it would be helping for you.
Thanks!