Scheduled Scan not completing.

Scheduled scan on my Windows7 Laptop sends a pop-up when complete, and then displays "view last scanning report" on the Scheduled Scanning page. On my Windows Vista desktop however, I do not receive a completed message, and there is no "view last scanning report" on Scheduled Scanning page. So appears not to be completing correctly, although says "last scheduled scan done within today" on the front screen. A manual scan appears to work OK, so why not the scheduled scan? How can I tell whether scan is running, has completed, etc ??