choghok wrote
How can I remove this warning?
You can remove ALL warnings by removing the call to tpl_msgarea() in the main.php of your template - though I really don't recommend to do that!
choghok wrote
Why should I get warning because of some configuration. This warning should be turned off as default.
The fact that you get this warning implies that the index menu of the battlehorse template relies on DokuWikis index function. Otherwise you won't get it. So I'd suggest to enable it again.