This thread was helpful for resolving a delayed wall warning that I was having, and I wanted to add something that may help others resolve these sorts of warnings quicker.
2 delayed walls warnings were showing up for plenum spaces whose wall constructions didn't look any different from those of other plenum spaces that weren't giving the warning. I clicked on the ceiling of the space just below the problematic plenum though, and found that it was set Next To the space it is a component of, rather than the plenum above. By fixing the ceiling's Next To to be the plenum space, the plenum's requirement of "at least 1 delayed floor and delayed wall" is met, and the warning goes away.

Holt Cutler, LEED AP