You are getting that error because the passwords for the SSL keys were encrypted under the old splunk.secret. If you copied one from another server the hash no longer works. You need to re-enter the password in the appropriate conf files and let Splunk re-encrypt it.
You should move
etc/users/... to capture all user data. The first directory hierarchy brings over shared objects and the second brings over private objects. Additionally you should configure authentication to yield the same set of users.