Have you tried running your project in Debug Mode (Ctrl-F4)?
You'll be able to see what's going on - if the Line sprite gets created, which animation/frame playing and so on.
If this doesn't help, try adding debug output. This could be a text objects somewhere on your layout. Make it big, set text wrapping=Character. Use Text->Append text to print some debug information to it. For example:
MyDebug -> Append-> "ActiveDots:" & NumActiveDots
or
MyDebug -> Append-> "Line:" & Line.UID & " picked:" & Line.PickedCount
Or you can use Browser->Log action for this.