Symptoms
Plesk login page shows one of the following error messages:
HTTP Error 500.19 - external Server Error
Error Code 0x8007000d
Config Error Failed to decrypt attribute 'password' because the keyset does not exist
Keyset does not exist (Exception from HRESULT: 0x80090016)
Cause
Insufficient permissions on the files:
 %ALLUSERSPROFILE%MicrosoftCryptoRSAMachineKeys6de9cb26d2b98c01ec4e9e8b34824aa2_*
 
 %ALLUSERSPROFILE%MicrosoftCryptoRSAMachineKeys76944fb33636aeddb9590521c2e8815a_*
 
Resolution
- 
Connect to the Plesk server via RDP. 
- Open the folder %ALLUSERSPROFILE%MicrosoftCryptoRSAMachineKeys.Note: Displaying of hidden files and protected system files should be enabled in Windows Control Panel > Folder Options. 
- 
Find files with the names that start with 6de9cb26d2b98c01ec4e9e8b34824aa2_and76944fb33636aeddb9590521c2e8815a_.
- 
Check access permissions on these files (right-click on a file > Properties > Security tab). Here are the correct permissions: System, Administrators, TrustedInstaller - Full control 
 IIS_IUSR, WMSVC - Read
 LOCAL SERVICE (if available) - Read
If the issue still persists, apply the following steps:
- 
Obtain a GUID: C:> reg query "HKEY_LOCAL_MACHINESOFTWAREMicrosoftCryptography" | findstr MachineGuid 
- 
Verify that the files have names 6de9cb26d2b98c01ec4e9e8b34824aa2_GUID and
 76944fb33636aeddb9590521c2e8815a_Example: If a GUID is: C:> reg query "HKEY_LOCAL_MACHINESOFTWAREMicrosoftCryptography" | findstr MachineGuid 
 MachineGuid REG_SZ 40c6fa54-0d9a-45ae-91c5-e85eb36dcbd2then files will have names: - 
6de9cb26d2b98c01ec4e9e8b34824aa2_40c6fa54-0d9a-45ae-91c5-e85eb36dcbd2 
- 
76944fb33636aeddb9590521c2e8815a_40c6fa54-0d9a-45ae-91c5-e85eb36dcbd2 
 
- 
- 
Restart IIS using the following command in a command-prompt: C:> iisreset