I presume you mean the OCS System Administrator interface? As said it is impossible to log on the system at all because of this problem. The machine is one of two networked at home. I can and have emptied the sessions tables using webmin
The Apache error log merely shows '[error] [client ::1] ocs2: DB Error: Duplicate entry 'rl2r4a0uiai4ealbf8a9avtj8273oqnhkhdt2jpu' for key 'sessions_pkey', referer: http://localhost/ocs/'
As far as I can see from the rest of the stuff I have copied above two procedures 'ADOConnection._Execute' and 'DAO.update' both seem to try to enter the same data into the sessions database table. Without looking into the depths of the code I do nto know whether this is the cause or one is called from the other.