Complete scan aborts before the end

When I run CAV to do a complete scan, it never reaches the end normally. When it is closer to the end of my folders (a particular big one) it quits with no message of any type. Normally it will show me a windows saying that scan is finished but it didn’t. If I run a scan on the same folders (not using complete scan but folder scan), it runs normally and find no virus.

When complete scan fails, I can see the HD led indicator stops for about 15 seconds (until then it was flashing rapidly, indicating the normal scan of disk) and immediatly closes the scan window, returning to the antivirus window with no warning.

What can be happening?

Thanks for your help.