AD Migration issues

When the functional level of the domain is upgraded, the password for the krbtgt system account is automatically changed. If you have an on-premises Exchange Server in your domain, this may cause it to stop due to authentication issues. After updating the DFL, you must restart the Kerberos Key Distribution Centre (KDC) service on all domain controllers:

  1. ERROR_DS_DOMAIN_VERSION_TOO_LOW 8566 (0x2176) – cause: a previous version of Windows Server exists.
  2. ERROR_DS_FOREST_VERSION_TOO_LOW 8565 (0x2175) – cause: the presence of previous versions of Windows Server on domain controllers in the AD forest: