What does this phrase meen? Does this meen that I should check DB replication and BARS options ? or something an other?
It just means you need to have a recent BARS backup handy if you want to restore your Callmanager. So schedule your Backup nightly (ie Mo-Fr at 03:00 am).
Second question: Should I keep the BARS archives remotely, not on the server? As I understand, BARS can be very useful to recover Web-configuration of CallManager?
Yes, that would be the Best thing to do. There is an option on the BARS Backup where you can specify the Netweork Location, Username and Password. That should do the trick.
Also you should check the BARS logs to see if the backup went well.(C:\Program Files\Cisco\Trace\BARS)