[2018] alpha 9 : Prefab uses the following forbidden blocks ?

Hello, I can not find what it is >> Prefab uses the following forbidden blocks : WalkwaySmallBlocks (Walkways & Railings) [ffffff]

Hello, I can not find what it is >> Prefab uses the following forbidden blocks : WalkwaySmallBlocks (Walkways & Railings) [ffffff]

Which prefab ? or prefabs ?

I cannot see any prefabs that have a message about forbidden blocks or appear red in the BP list.
Was it spawned in Before A9 ?

Ok can you download this copy of it it should be ok now & replace the original BP of it when save in A9 -

let me know when you have downloaded it so I can remove the link. Thanks.