When searching for a circle by zip code (78733) I got:
user warning: Column 'nid' in field list is ambiguous query: SELECT COUNT(DISTINCT (nid)) AS count FROM node n INNER JOIN location l ON n.vid = l.eid INNER JOIN node_access na ON na.nid = n.nid WHERE (na.grant_view >= 1 AND ((na.gid = 0 AND na.realm = 'all') OR (na.gid = 1 AND na.realm = 'term_access'))) AND ( l.type ='node' AND l.latitude > 29.967968269 AND l.latitude < 30.691439731 AND l.longitude > -98.294196696 AND l.longitude < -97.456003304 AND (IFNULL(ACOS(0.863133871022*COS(RADIANS(latitude))*(-0.137014070551*COS(RADIANS(longitude)) + -0.99056910131*SIN(RADIANS(longitude))) + 0.504975168394*SIN(RADIANS(latitude))), 0.00000)*6372663.41298) < 40233.68) in /home/spiralscouts.org/public_html/includes/database.mysql.inc on line 172.
Maybe you need to specify DISTINCT(n.nid)?