Unable to add `Resources` as a column to Gantt chart

I’ve used GP on and off over the last couple of years and now I’ve made the decision to use GP for all my project and timeline efforts. I have a new project and when I attempt to add the Resources column to the Gantt chart using Manage Columns... many of the columns, including the Resources column are greyed out and I can’t select them to add the column to the chart.

See snapshot http://pwc-lms.com/OpenStuff/GanttProject/resources-greyed-out.png

Than you so very much, yes the user interface was a little confusing but, your explanation make it very clear what to do.