Error not letting me access admin page

Heya,

I added an add-on domain today, and installed wordpress to it. Everything was going fine until i switched templates in the wordpress admin dashboard. Even after that, things seemed ok until i tried to create a new page... things started going VERY slow, failing to load, and kept giving me this error,

"Warning: Cannot modify header information - headers already sent by (output started at /home/mowattc/public_html/tanishagupta.com/wp-content/themes/build-lite/inc/about-themes.php:9) in /home/mowattc/public_html/tanishagupta.com/wp-includes/pluggable.php on line 1228"

I cleared my cache and rebooted my computer and modem just to be safe... when I even tried to just type in the url of the site i'm working on , http://tanishagupta.com , it did finally load, however, when i add the /wp-admin to the end, it just gives me that error above.

Any thoughts on the problem?

Thanks

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