Not able to log into website – Warning messages

Hi, I am also not able to log into my wordpress website – mishofilev.com . As soon as I enter my username and password I get these warning messages. I believe these errors began once I changed my theme to the current one on the website.

Warning: include_once(includes/custompost.php) [function.include-once]: failed to open stream: No such file or directory in /home/content/00/9956000/html/wp-content/themes/architekttheme/functions.php on line 498

Warning: include_once() [function.include]: Failed opening ‘includes/custompost.php’ for inclusion (include_path=’.:/usr/local/php5_3/lib/php’) in /home/content/00/9956000/html/wp-content/themes/architekttheme/functions.php on line 498

Warning: Cannot modify header information – headers already sent by (output started at /home/content/00/9956000/html/wp-content/themes/architekttheme/functions.php:498) in /home/content/00/9956000/html/wp-login.php on line 362

Warning: Cannot modify header information – headers already sent by (output started at /home/content/00/9956000/html/wp-content/themes/architekttheme/functions.php:498) in /home/content/00/9956000/html/wp-login.php on line 374

Warning: Cannot modify header information – headers already sent by (output started at /home/content/00/9956000/html/wp-content/themes/architekttheme/functions.php:498) in /home/content/00/9956000/html/wp-includes/pluggable.php on line 680

Warning: Cannot modify header information – headers already sent by (output started at /home/content/00/9956000/html/wp-content/themes/architekttheme/functions.php:498) in /home/content/00/9956000/html/wp-includes/pluggable.php on line 681

Warning: Cannot modify header information – headers already sent by (output started at /home/content/00/9956000/html/wp-content/themes/architekttheme/functions.php:498) in /home/content/00/9956000/html/wp-includes/pluggable.php on line 682

Warning: Cannot modify header information – headers already sent by (output started at /home/content/00/9956000/html/wp-content/themes/architekttheme/functions.php:498) in /home/content/00/9956000/html/wp-includes/pluggable.php on line 881

This is my first time using WordPress , any help would be greatly appreciated.