I was getting a very similar error...
Duplicate entry '14-6' for key 'PRIMARY'
SQL=INSERT INTO `#__finder_links_terms4` (`link_id`, `term_id`, `weight`) SELECT 14, `term_id`, ROUND(SUM(`context_weight`), 8) FROM `#__finder_tokens_aggregate` WHERE `map_suffix` = '4' GROUP BY `term` ORDER BY `term` DESC
...and solved this by clicking the 'Clear Index' button at the top. After that I was able to index my files.
