Cool, I have tried the Level 48 trick now...

That's because in Level 9, you moved to much...

That's why he tried to go throught that door in Level 10...

When playing Level 9, You have to stop in just 5-7 seconds and go get that key...

When you're in Level 10, You now have some time to get that key on the top right, because your "Guest from Level 9" is just standing there for like 5-7 seconds before going to the next level.