On Windows, creating an instance for any configuration registers a service-id with Windows services. If the service-id exists, there is a service-id conflict and the instance creation fails. For example, you might migrate a 6.0 or 6.1 instance named foo. If the foo service-id exists, the creation fails.
To avoid the conflict, during migration, change the configuration name using either the CLI or the Admin Console. Another option is to copy the configuration to a new configuration that uses a unique service-id. Use either the wadm> copy-config command, or the Copy button on the Admin Console Configurations page to copy the configuration.