I am currently unable to select more than one object at a time for some reason. I have object mode selected. I then use shift + LMB (mouse buttons swapped from Blender 2.78 default). But the select just moves to which ever object I select and deselects any object I had already selected. I also tried box select, which now selects nothing. I have applied transformations as I know unapplied transformations can make things screwey. It was working just fine earlier. Any help would be much appreciated.
In the outliner if you accidentally type while renaming (without having renaming properly started) you can mess up the selection enabled flags.
Type 'a' to 'select all' (in the outliner) and then 's' to re-enable the selection enabled icons (arrows between eye and camera).