Possible Child Template Bug

Here is the case,

When I switch to child template most of, but not all, of shortn links are blank screen with following error in my log:

PHP Warning: Cannot modify header information – headers already sent by (output started at /home/newday/public_html/mysite.com/wp-content/themes/theme-child/functions.php:51) in /home/newday/public_html/mysite.com/wp-includes/pluggable.php on line 1210

but when i switch to my main theme all shortn links works fine.

any help will be appricated