Quicktime don't play my m4p files

Question

Hi, I used the 64bit Version of iTunes & Quicktime (9.0.1.8). My computer is activated for playing my purchased songs. Within iTunes I can play all my songs without problems.
But when I open my m4p files directly with the Quicktime player I got the message, that I was not permitted to play this song on this computer.
If I open iTunes to carry out the activation, I get the message that the computer is already activated. However, QuickTime nevertheless does not play the song.
Uninstall and reinstall iTunes & Quicktime does not help.
Any other idea?
Grettings

Answer 1

What do I do?
Frankly, if you have deleted the original movie clips from your camera/camcorder and iPhoto, then it sounds as if you are up the proverbial creek without a paddle and there is nothing further that you can do.
Some facts:
For some reason, the movieclips are awful small (13-30 KB).
640 x 480
Codecs: H.264, AAC
While these facts are of little value without file duration information, as you yourself have already noted, the file sizes quoted are extremely small. A typical VGA H.264/AAC file of reasonable quality would normally have a combined total data rate in the 700 to 1,700 Kbps range depending on specific settings, profile, and level of the encoding software and could be even higher or lower depending on the quality levels required. Therefore, it is reasonable to assume that files in the 13 to 30 KB range only contain 104 to 240 Kbs and either have durations measured in fractions of seconds or do not actually contain enough data to be played. (E.g., the video data may be missing or the file is corrupted.) Thus, it is most likely that something was wrong with the workflow used to "export" your files to the external drive and when you ignored the fact that the files were not playing correctly, you closed the door on anything that you could do when you deleted the source files. (I.e., the normal workflow here is to copy the entire iPhoto library to the external drive, switch libraries, confirm the new library is working properly and only then delete the boot drive copy of the iPhoto library.)
OBS: When I try to convert the files into something else (AVI, MP4 whatever) either it comes with an error, nothing happens or the converted file wont open. This happens with various convert-programs.
If the data in the files is missing, then there is nothing to be converted by any application.