Aha I found the problem
Instead of calling the Reset method on the DataTable, you need to just dispose it and create a new DataTable. So your code would look like this:

Code:
dbTable.Dispose()
dbTable = New DataTable
DataAdapter.SelectCommand.CommandText = "select * from Customer"
DataAdapter.Fill(dbTable)
DataGrid1.ItemsSource = dbTable.DefaultView
Does that make it work how you want it to now?