Animated lines

I'm trying to make some animated lines in flash, but can't get it to work properly. What I do is create a line maybe 2 inches long, then I want it to merge with three other lines making a square in the end. My problem is that I don't seem to get a motion tween. I make the line in keyframe one, then I make a new keyframe at say 10, at 10 I move the line down to were it's supposed to be, and shorten it a bit, but the tween wont work. What am I doing wrong here? is it imposible to animate lines?

Btw I'm using Flash MX

You'd need to supply more information for a better suggestion... but... are you right clicking on Frame 1 and selecting 'Create Motion Tween' AND Frame 10 and selecting 'Create Motion Tween'??

If the line from Frame to Frame is a dashed line... you're not there yet.

It's also generally easier to make your line a symbol (Graphic) before tweening it. FMX, and I think F5 as well, don't have a problem with 'un-symboled' vector graphics... because they make the vector graphic a symbol witha a generic name for you.

If it's a drawn object then you need to use Shape Tweening.

If you make the line into a symbol (select the line, click Insert > New Symbol and then give it a name) then you can use a motion Tween on it.