sometimes it shows movies, sometimes not

[yarrow3000]

hi there, i have a html- based website and when you click certain buttons, small popup-windows appear and show movies, which were mpeg movies that i imported in flash mx.
now on some machines everything works out properly, on others, the movies are not displayed. but on all machines is the flash player 6 plugin installed.
why o why???

[mraspiller]

Is there a movie player installed on all machines...that my be the problem