Following the y coordinate only

It has to be simple… err ok. I have a rocket launcher. I know how to make it follow the mouse… but I only want it to follow the y coordinate. I need the x position to stay locked, so the launcher will only move up and down with the mouse.

so, simply thinking, I put this on the launcher:

[AS]onClipEvent (enterFrame)
this._y = _ymouse


when I preview the movie, it just dissapears

sigh why?

after that I tried all kinds of things relating to stopping and start dragging, hit testing various movie clips, etc. and nothing works right.