Reset the datamember as well as the datasource. Set the datamember to a blank string before attaching to a new datasource. It's trying to use the old datamember on a new datasource and will throw ...

Let the user know what direction their data is sorted in when using a DataGridView.

Upon doing a Step-thru trace of my code, I'm finding that the changes to the values made in DataGridView are not actually bound to the XDocument object and as such, do not propagate back.