Step-By-Step: Migrating Active Directory Certificate Service From Windows Server 2008 R2 to 2019

If ADCS wont start after restoring the backed up CA and importing the registry file and you receive the error "The system cannot find the file specified. 0x2 (WIN32: 2)", you should check the CACertHash value in the registry. The back up function will not back up old expired root CA certs but they will still exist in the registry values and produce an error (since the certs don't exist). You can resolve this by replacing each outdated cert thumbprint value in the CACertHash entry with a dash "-". In my case I had two previous expired thumbprints present and replaced them with 2 line separated dashes, leaving a third line with the current cert's thumbprint. 

e.g.:

-

-

89 14 89 c1 cd 30 23 b1 99 99 99 5e 2d d6 09 e5 2b 9a 3c 60

Adam