Blender only plays one action in the NLA editor - ignores others

I’m hoping someone can help me. I’ve been following a tutorial on creating a walk cycle, which can be seen here:

I have created a simply walk cycle that I’m happy with. The problem I have is that when I go to create “forward motion” action (seen at about the 09:30 point in the vid) which is supposed to move the character forward while the walking cycle plays, nothing happens! I can have either the walk cycle play while the character is stationary OR I can have the character move across the screen but the walk cycle doesn’t play. It appears that it’s one action or the other. I want both actions to play. Am I missing something really obvious? I’ve attached the blend file.

Ok I solved the issue. The “Channel mute” button was switched on. Duh. I had no idea what the icon was supposed to represent - seems silly having a speaker to represent something completely unrelated to sound! I must have toggled it by accident. Anyway, that’s what the problem was.

Try checking that the upper channel is set to “add”.