Scanning does not take place

After setting up my Norton NAV2009, ( as far as  know, I have alI the updates installed) I set it up to run a complete scan daily. It worked for about a month but now it wont recognize the scan anymore and scan. I have tried to turn it to various schedules: every 2 days, weekly, etc. but ti still will not automatically run. I have checked the setup and even defaaulted all and reset them to where I wanted them. Has this happened to anyone else? Please advise how I can get this working again. Thank you. I am running WindowsXP SP2 and my norton is 16.1.0.33. It makes me feel so vulnerable :-)