I have completed all Levels of the first three stages in order an everything went fine. Then i have completed the first 5 Levels of Stage 4 also in order, but because of the fact that i was already tired and the later levels need more concentration i decided to go to bed and try it the next day.

Yesterday i started Switchball, thought about going for a warmup-round and a quick achievement and went for a silver medal in level one. I got it, so i went back to Stage 4 Level 6. I finished this level but a screen tells me:

Level completed

to proceed to the next Stage you will have to have completed all earlier Levels.

Hm?? Ok, i tried it again, and same thing happened again. Stage 5 doesn´t unlock and the achievement for completing Stage 4 doesn´t unlock either. Why? Do i have to complete Level 1 to Level 6 in order?

Thanks in advance  

are u sure u have completed every level by going into the finish at the end? it should unlock it, its probably a glitch, cant help soz

if i wouldn´t have finished every level how could i start with the 6th one in this stage?

I have the exact same problem except i'm stuck in Iceworld.  I've gotten through all 6 levels in that world, but it says I can't unlock it until I finish all of them.  Any luck on your end as to what the problem is?

Why don't you just delete your save and start over? It won't take long as you'll know what you're doing on each level.

This is how if have finally found out what was wrong:  i noticed, that if you press "x" in the mission-menu it is possible to compare your time on each stage with your friends. According to this, i was missing the 6Level in the 3rd Stage. I can´t understand how this has been possible cause i have gotten the achievement for completing the 3rd stage.

Complete the last level over again and it should unlock the next world.

I had the exact same problem, with my 3rd stage level 6 not being shown as completed, even though i had the achievement. sort of a strange glitch

I have the same problem - after completing Level 4-6, the Stage 5 Lavaworld is still locked, and it tells me I have not completed all the levels.
Does that mean I should do all the stages again - starting from Level 1-1, all the way to Level 4-6 again???