Thanks for reporting this. I have opened an issue on this and will try to fix it.
I'm not sure what went wrong.
Can you be more specific about how you got this error to happen? From the callstack it looks like the last thing you did was click in a cell of the bottom row of the grid. What did you do right before that? How exactly were you copying the values from Excel?
I recently fixed a different exception in the same dialog which would happen if you clicked on one of the column headers in that dialog. (This will be fixed in the next Skyline Daily build). But the error you're seeing is different.