It could be that the layer the elements are on is locked or hidden, or the elements themselves could be locked.
When you select that row, there should be a warning at the top of the schedule screen next to the buttons for selecting elements in plan or 3D (these will be locked as well).
Barry.
One of the forum moderators.
Versions 6.5 to 25
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10