I seem to be having the same problem. Although both my version of WordPress and BruteProtect are the latest versions, when I try to call for an API key, I get the following error:
Warning: call_user_func_array() [function.call-user-func-array]: First argument is expected to be a valid callback, ‘BruteProtect_Admin::bruteprotect_warning’ was given in /home/kenand6/public_html/webdirectoryreviews.org/dir/wp-includes/plugin.php on line 406