IIS Admin Service allows IIS metabase administration which is used to store SMTP and FTP configuration. If you see this service stopped in the Services window, server will be unable to configure SMTP or FTP.
When you try to start IIS Admin Service, this error message may be displayed:
Windows could not start the IIS Admin Service on Local Computer. service-specific error code -2146893818.
The Event Viewer also records a similar message:
The IIS Admin Service service terminated with the following service-specific error: Invalid Signature
This error occurs when the machine key which is used for decryption/encryption is corrupted. You will probably see numerous Schannel errors because of this corrupted file. Here is what to do to make sure of the root cause:
Go to MachineKeys folder (C:\ProgramData\Microsoft\Crypto\RSA\MachineKeys)
Check the Last Modified Date of the file that has a name starting with c23
If the date is newer than the date IIS server is installed, it means something (an update or installation) caused this file to change and get corrupted
Follow the possible solutions below in the given order.
Restore machine key
If you have a backup of the machine key starting with c23, restore it to the MachineKeys folder.
Some resources also recommends restoring the Metabase.XML and MBSchema.XML from History folder (C:\Windows\System32\Inetsrv\History)
Reinstall IIS 6 Metabase Compatibility
If the restore option doesn’t work, follow the steps below to reinstall IIS 6 Metabase Compatibility feature. This feature recreates a machine key.
Remove the machine key starting with c23 (C:\ProgramData\Microsoft\Crypto\RSA\MachineKeys)