I get errors, can't do anything

Hi, I get this message in the backend all the time: Warning: simplexml_load_string(): Entity: line 1: parser error : Start tag expected, '<' not found in /mnt/webi/d2/76/53465376/htdocs/xxxxxxxx/wp-content/themes/simple-catch-pro/update_notifier.php on line 120 Warning: simplexml_load_string(): Access denied. Your IP address [81.169.144.135] is blacklisted. If you feel th in /mnt/webi/d2/76/53465376/htdocs/xxxxxxxx/wp-content/themes/simple-catch-pro/update_notifier.php on line 120 Warning: simplexml_load_string(): ^ in /mnt/webi/d2/76/53465376/htdocs/xxxxxxxx/wp-content/themes/simple-catch-pro/update_notifier.php on line 120 Warning: Cannot modify header information - headers already sent by (output started at /mnt/webi/d2/76/53465376/htdocs/xxxxxxxx/wp-content/themes/simple-catch-pro/update_notifier.php:120) in /mnt/webi/d2/76/xxxxxxx/htdocs/illibode/wp-includes/option.php on line 568 Warning: Cannot modify header information - headers already sent by (output started at /mnt/webi/d2/76/53465376/htdocs/xxxxxxxxx/wp-content/themes/simple-catch-pro/update_notifier.php:120) in /mnt/webi/d2/76/53465376/htdocs/xxxxxxx/wp-includes/option.php on line 569 What to do now?