Why would you assume that
i
is valid for both
dataGridView_auswahlen
(row source) and
table
(row destination)?
Since you are only transferring selected rows, unless your selection always starts with the first row and has no gaps, you will always get an exception.
Instead of using an index, create a new row using
DataTable.NewRow[
^], and add that to your DataTable. You can then use the DataRow object to add your cell values.