unserialize error in multisite configuration

[c4i]

Hi

I'm using CiviCRM 4.3.6, on Drupal 7.23 on a SUSE 11 Linux/MySQL virtual server.
I have setup a multisite system for AUS and NZ.
I have setup the permissions groups/organisations matrix so AUS can only see AUS contacts and NZ can only see NZ Contacts.

All appears to be working so far. However, on my second site, domain ID 2, I get the following error at various times. It doesn't have any obvious consequences.

    Notice: unserialize(): Error at offset 205 of 212 bytes in CRM_Core_BAO_Setting::getItem() (line 209 of /srv/www/htdocs/drupal/sites/all/modules/civicrm/CRM/Core/BAO/Setting.php).
    Notice: unserialize(): Error at offset 202 of 209 bytes in CRM_Core_BAO_Setting::getItem() (line 209 of /srv/www/htdocs/drupal/sites/all/modules/civicrm/CRM/Core/BAO/Setting.php).

Can anyone help to identify the problem and/or solve it please.
Thanks
Eric.