Wow, a lot of people have had problems with this achievement. On my old profile, it unlocked on the bridge crossing on the way to the boss fight. This profile however is a different story. Gonna try the solutions in this thread later and see if I have any joy. Last one for the 1000g.
If you play Project Spark, and have worlds you would like an up vote on, a remix and a like. Even a follow. Just message me on XBL with details. Would appreciate a return.