What Type Of Objects Prevent Creating A Block?

[MarkMc]

Trying to swap a few cabinet configurations to a new plan and have some that I can't make an architectural block. What type of objects prevent blocking?

[MarkMc]

I found it- Just kept shift selecting different types of object until it allowed for a block.

Turned out there was a cad line in there I couldn't see- must have been placed to get a dimension to snap to for something else it wouldn't.