Cannot read session record

Hi.

After a database migration I am getting the following message in the apache logs:

[Sat Apr 12 22:20:16 2014] [error] [client clientIP] Cannot read session record, referer: https://mydomain/login/index.php

In the Moodle activity record it seems that the user is trying to login when this message is produced.

Any ideas of what can cause this and what is the consequence? The authentication method is LDAP.

Thank you.