I got this error when I activated the plug-in. Originally I had the wp-people-admin.php in the plug-in file (per wp-people-Readme) and it came up with the error the other person above had. Then I left it just in the admin file (per the Readme) and this is what happened:
It still says it was activited.
Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /homepages/22/d95365795/htdocs/wordpress/wp-content/plugins/wp-people.php on line 85
Warning: Cannot modify header information – headers already sent by (output started at /homepages/22/d95365795/htdocs/wordpress/wp-content/plugins/wp-people.php:85) in /homepages/22/d95365795/htdocs/wordpress/wp-admin/admin.php on line 6
Warning: Cannot modify header information – headers already sent by (output started at /homepages/22/d95365795/htdocs/wordpress/wp-content/plugins/wp-people.php:85) in /homepages/22/d95365795/htdocs/wordpress/wp-admin/admin.php on line 7
Warning: Cannot modify header information – headers already sent by (output started at /homepages/22/d95365795/htdocs/wordpress/wp-content/plugins/wp-people.php:85) in /homepages/22/d95365795/htdocs/wordpress/wp-admin/admin.php on line 8
Warning: Cannot modify header information – headers already sent by (output started at /homepages/22/d95365795/htdocs/wordpress/wp-content/plugins/wp-people.php:85) in /homepages/22/d95365795/htdocs/wordpress/wp-admin/admin.php on line 9