Not all objects selectable

In the attached model not all objects can be selected in the view port. Mainly these are object that are children of the Basement empty save the windows. This however cannot be the reason.
I have no I idea how this got messed up or how I could fix this. The one way I perceive is to import the objects into a new blend file. I would hover like to learn the cause of this, so I do not make the same mistake twice.
Really annoying is this because all object are gathered in a group, but when I try to move the group only the windows and the balustrade move.

Attachments (1.6 MB)

Look in the outliner window. Some of the models have had their selectability disabled, the arrow icon is greyed out. Press the icon to re-enable it.

Thanks Richard. If all my problems were solvable in such an easy manner 8)