Make sure your virus signature files are up to date and run your AV program over a few of these files which refuse to comply. I would also take advantage of all the free trial versions of other brands of AV that you can get and use them to check that no viruses or such have sneaked past NOD and infiltrated your system. Also read as many of the "Sticky" posts as you can... Quite often people have found a solution to their problem among these. It could be that these files are not genuine movie files and your system is rejecting them for a legitimate reason.