Nether core not working

Nether core not working says all players have to be close.

*What I expected to happen was... It should have made nether rack surrounding the area

*What actually happened was... Nothing. It turned up with a sign saying all players had to be there. Note: I've never played multiplayer on that map

Steps to Reproduce:
1. Create nether core, 14 cobblestone, 4 gold blocks
2. Arrange in correct pattern
3. Try to activate