Duplicate entry in access log

I am getting loads of error messages like this -

“Duplicate entry '768150' for key 1 query: INSERT INTO accesslog (title, path, url, hostname, uid, sid, timer, timestamp) values('Events', 'event/2006/09/16/day', '', '66.249.70.228', 0, 'e0cb8d80cdd5c40fb38b8c1c932d5754', 468, 1183620941) in /home/healhead/public_html/includes/database.mysql.inc on line 121.”

They all relate to '768150' in accesslog.

I can see, from Myphpadmin, that 768150 is the last entry in the primary key for the accesslog table. Autoincrement seems to be enabled for this field (but how would I know if its working?).

I have not done a db dump or import of any kind recently.

I have read the many posts on duplicate entries and tried the following –

1. empty the sessions table (http://drupal.org/node/141886). No change.
2. change the entry in the sequences table to a number higher than '768150' in the aid field (http://drupal.org/node/69722). No change.

Any ideas what I should try next?

Thanks
Nigel
Community Plumbing for Headingley, Leeds UK
www.healheadingley.org.uk