Why cant i pack the apk?

this is the description
and there's no error in blocks
help how to fix it

You probably have red bugs in the lower left corner. You used the "back" event twice.

Rename your components to something other than just back

but i dont have a components name back on screen2
by the way, most of the bottoms, lables etc. I name them in Chinese Traditional

Look in screen 'end'

It work!
I appreciate for your help !