How do you add columns to the DataGridView? At design time or at run time by code? How do you know the scroll bar is there when the datagridview is being populated?
If the columns are added at design time (with "Add Column" and "Edit Columns" dialog box in VS), when the total width if all columns is greater than the width of the DataGridView, does the scroll bar appear? It should, unless there is one or more columns' "AutoSizeMode" is set to "Fill", which would shrink one or more columns' width so that all columns would fit the DataGridView, thus no scroll bar is needed.