Two gotchas I've seen come up a few times lately.
Revit 2015 R2 provides a separate button for a new Data Row when we create a room, area or space (sheets too). It is disabled however when the schedule is not using the Itemize every instance option (un-checked). This means creating a new row might not be visible in the schedule, so it is disabled. I wrote a post about the new Data Row button when R2 became available.
Can't select something in your view? Did you pin it? Someone else pin it? Why do I ask? Because we can tell Revit we don't want to select Pinned Elements now. The trouble is we forget those settings easily and later we look clicking challenged when we repeatedly click on something and Revit ignores us. I previously wrote about the new since Revit 2014 Selection Options.