[10.5] I declared this variable global, but now I can't access it. Why?

Global variables must be declared in every script that uses them. For instance, if your movie script contains the following:

global helpFrame

on startMovie
  set helpFrame = 100
end startMovie

and you have a button in frame 20 that needs to use the value of helpFrame,

on mouseUp
  go to helpFrame
end mouseUp

is not sufficient in the sprite script (you'll probably get a warning like "Variable used before assigned a value" when you compile the script). You need to add

  global helpFrame

at the top of this script as well before it will work.