I see "External Grade" selected on one of the Grade Center columns in the Grade Center.  How can I remove that?

You cannot completely remove "External Grade" notifications from the Grade Center.  Each time a new course is created in Blackboard, one column is already designated to be "External Grade" and it is more than likely the "Total" column.  "External Grade" refers to a module that students can activate on their home page of their account called "Report Card" module.  "Report Card" takes all of the "External Grades" from their classes and creates a report card for them to see all of their current grades in 1 view, similar to a report card from the grade school days.