Although I have chosen from the settings to ''Install security updates without confirmation'' The updates are not installed and I am not notified .I have checked this a couple of times.I have seen posts about this situation on the Ubuntu forums but there was no solution.Is there anything you could recommend me to do.Is there any other setting I have to modify?
There was an update to this issue released by Ubuntu but its working in some and then we have cases like yours where its not working.
You could always just cron an aptitude update && aptitude upgrade. There is a script I started a year or so ago on my blog, its a start.