I had exactly the same symptoms with KIS 2012. On my computer, I have three hard disks, one of them is the "data" disk with some big PST files. Initially I had configured the full scan to scan everything, and I thought the setting "do not run for more than 30s per object" would take care of any "getting stuck" problems, but anyway, my scan always got stuck on "xnacc.sys". Thanks to that file name, I found this discussion thread. I have changed the settings and now the full scan completes in half an hour. Of course it is no longer scanning eveything, as it excludes backups, email, large files, etc. Thanks to the previous posters for their advice! But I am afraid the setting "do not run for longer than X" is not working as I would have expected.