Cannot modify header information - cannot be resolved though no errors [duplicate]

This question already has an answer here:

• How to fix “Headers already sent” error in PHP 11 answers

I am facing a problems with my wordpress site and i cannot see anything on my login screen : http://vtrails.us/login - It's blank. But in my error_log file i am looking a problem

PHP Warning: Cannot modify header information - headers already sent by (output started at /home/vtrailsu/public_html/wp-content/plugins/mix-tape/update_calls.php:198) in /home/vtrailsu/public_html/wp-includes/pluggable.php on line 1228 But I cannot see anything on update_calls : line 198 (see above) So what can be it's solution? Can i get more information about it?

via Chebli Mohamed