Issue with loading custom building into world editor, what am I doing wrong? Saved building locally.

[canmonkeydo]

When loading them in prefab editor it works just fine except for one block showing as the clear blue box with a question mark

The prefab was saved from a server I run 

 

[Riamus]

When loading them in prefab editor it works just fine except for one block showing as the clear blue box with a question mark

The prefab was saved from a server I run 

That question box means a block is used that isn't compatible with the current version of the game.  Replace it.  As long as you have any of the blocks, the prefab will not load into the game.