welcome to the forum!
Do you have a "mouseup" handler anywhere in your STACK or in a CARD script?
Usually this does not happen, so the problem must be somewhere else.
Did you import it via menu: File -> Import as control?I inported a video and this won't play.
Then you need to script the playback of the video!
So you may use a PLAYER object instead. This also provides a basic navigation bar
to play, pause, stop, forward and rewind the video.
All this must be scripted with an imported videofile.
The PLAYER object only supports external audio- and videofiles.
Best
Klaus