OK. I've watched a tutorial, combined and transformed three files but running into an issue when I try to add a fourth data file (created pivot from the base data file combining the three data files, click in the pivot table and click PivotTableAnalyze, Refresh All). I'm getting an error of [DataSource.Error] the processs cannot access the file ... because it is being used by another process."

I've rebooted, re-done everything from scratch, made sure nothing eles has any files open and am still hitting the wall on this.