"Ceiling values may not be changed..."

[Keith_K]

"...as the floor above this room has varying heights".

This is the message I get when I try to change the ceiling heights of the rooms on the ground floor of a section of my plan and the fields I want to change are greyed out. I don't understand it.

I have painstakingly checked the values of all the rooms of the first floor in Room Specification > Structure and they are all identical (e.g. Ceiling (B), Floor (C), Rough ceiling, Finished Ceiling, Ceiling below (H) etc).

Why then am I getting this message?