Here is the link to the sample file in question: Dropbox - The Post.m4v
Sorry! It appears someone decided to edit/remove the link's URL reference before I was able to download the file for examination. Looks like you'll have to perform the examination for yourself. Basically, you need to use either a video player app or a media utility app (e.g., MediaInfo or the QT7 Pro "Properties" window) to confirm whether your M4V files contain an AC3 audio track. (Unfortunately, some apps—e.g., VLC—misidentify AC3 audio as "surround" even when it is encoded as stereo.) If so, check to see if those files with 5.1 surround sound load/play correctly but those with non-surround (mono, binaural or stereo) audio refuse to open. If your files are following such a pattern, then it would seem you still have a codec conflict at work. If not, then your issue is probably something else.
I didn't use handbrake to make this file.
Used HandBrake merely as an example since you did not mention what workflow was used to create your files. (I.e. HandBrake is free, very popular, and, by default normally adds a secondary AC3 audio track to M4V outputs when using the higher quality presets.)
I removed the components from the following location: Macintosh HD>Library>Quicktime
Believe that is the correct global add-on target folder as opposed to the "~/System/Library/QuickTime" folder that contains the system installed codecs. However, did you also check your local user "Library/QuickTime" folders to ensure no latent/active codecs are installed that might create conflicts?
I also noticed when I did a Get Info on the file I got a message:.. Neve seen that message before.
Have never seen this message either and am confused as to why it refers to QL (QuickLook) rather than the QT (QuickTime) app/structure use.
Let me know your thoughts.
Without actually seeing the file, long-distanace diagnosis is often little more than a guessing game.