What theme were you using before you deactivated BP and BP template pack? Go to server and rename wp-content/themes/YourActiveTheme to something like wp-content/themes/YourActiveTheme-xxx so that active theme will revert to WP default theme
You need to visit the themes page to ensure you have reset themes before logging out or trying to visit the frontend as the BP theme was still in effect operational in WP eye’s
rename the folder of your current theme, if not work ,
try to reset the theme from database : http://docs.appthemes.com/tutorials/how-to-change-wordpress-themes-directly-from-the-database/
Or
try rest all plugins from databse
UPDATE wp_options SET option_value = ” WHERE option_name = ‘active_plugins’;
http://perishablepress.com/quickly-disable-or-enable-all-wordpress-plugins-via-the-database/
erm no lets not advise people go and directly edit DB 
But if you do, always mention to “backup database first” otherwise ….
Yes of course, but it is just an update 
and in many case’s, this solution is last and the easy way restore site
Thank you all for the suggestions. The theme is Atahualpa 3.5.3. I renamed the theme, but still not work. However, I haven’t tried resetting the theme or plugins from database.
Hugo,
I am not sure whether I understand “You need to visit the themes page to ensure you have reset themes before logging out or trying to visit the frontend as the BP theme was still in effect operational in WP eye’s” correctly. Do you mean “when I disable buddypress, I need to go to my site’s front page, then log out”?
One of the drawbacks of a plugin that requires it’s own theme located within the actual plugin is that if you deactivate the plugin then immediately try and visit the front of the site you will throw an error as WP still has the bp-default theme listed in the DB as the current theme; a child theme has an approach it can take to programmaticaly switch the theme back to the WP default if BP isn’t active.
We revised that code to work correctly as it exists in the BP default theme but it can’t run from that functions.php file but would work if copied to child theme functions.php.
Otherwise after deactivating BP you need to next access the theme page in the dashboard and if not showing a WP default select one before trying to view the frontend of the site.
