Dropbox-backup plugin log issue

Hi everyone,
My website is not connecting to the database, if I go in the cpanel on my hosting account on the log error is showing me the following :

[Fri Jul 10 13:23:28 2015] [error] [client 176.61.42.120] PHP Fatal error: Call to undefined function wp() in /usr/local/pem/vhosts/375920/webspace/httpdocs/butterfly.design/wp-blog-header.php on line 14
[Fri Jul 10 13:23:34 2015] [error] [client 176.61.42.120] PHP Fatal error: Call to undefined function wp() in /usr/local/pem/vhosts/375920/webspace/httpdocs/butterfly.design/wp-blog-header.php on line 14
[Fri Jul 10 13:23:40 2015] [error] [client 176.61.42.120] PHP Fatal error: Call to undefined function nocache_headers() in /usr/local/pem/vhosts/375920/webspace/httpdocs/butterfly.design/wp-admin/admin.php on line 33
[Fri Jul 10 13:23:47 2015] [error] [client 176.61.42.120] PHP Fatal error: Call to undefined function nocache_headers() in /usr/local/pem/vhosts/375920/webspace/httpdocs/butterfly.design/wp-admin/admin.php on line 33
[Fri Jul 10 13:25:52 2015] [error] [client 176.61.42.120] PHP Fatal error: Cannot use object of type WP_Error as array in /usr/local/pem/vhosts/375920/webspace/httpdocs/butterfly.design/wp-content/plugins/dropbox-backup/libs/lang.class.php on line 83

website link is https://www.butterfly.design

I am not a programmer so I dont know what I should do, if anyone knows would be much appreciated
Thank You !