I shot 4 movies on my Nikon D5000. Downloaded them to my computer as .AVI files. Two play fine in Quicktime and VLC 2.0.2. The other two fail in DivX, Quicktime and VLC, displaying messages indicating unknown formats. All the movies play with MPlayerX.
One of the problem movies is shared from https://www.dropbox.com/s/r9cjy9y22u1ke3r/DSC_6095.AVI.
Nikon Support says they can play the Dropbox copy but did not say with what program or the codecs they used.
VLC gives a large number of error messages in its logs. I suspect the files are somewhat corrupted on the camera but cannot get this verified.