The forth button in game object not work

I have problem liek this,
I have game object which i hold other button. I use some script to make it move up and down when pause or unpause.
When i create the first, second, third, forth button, they all interacable. But in the fifth one, i cant interac with it. even i use the preset button when use create gameobject->UI->Button.
I dont know why is this happen. But if I move it our of this game object, it can work fine.
Is that becuase i use free unity version and it limit how much i can use ?

Make sure you only have the “Canvas” component attached to the main canvas object, if you have this component attached to a panel or another UI element, buttons inside other UI objects won’t work.