check
www.nepalbb.com
I am newbie so cant figure our whats the problem there.
I was editing the index page before this error appeared.
now i cant go to admin panel and i dont know how to fix the error through file editing, I only can edit the pages through admin panel
I believe this is a server error, nothing to do with MyBB.
However, I suggest reuploading the index.php and see if that changes anything. If not, contact your webhost and tell them your problem.
i was editing the template so i thought this is mybb error
I doubt a template change would do that, and I have seen the same thing happen with my site. Its most likely a server error.