I think this bug has already been fixed in this commit: https://github.com/brainstorm-tools/brainstorm3/commit/8cf257913359a5ee5554a9d3cf2036ef8eb03b95
This was already documented in this forum thread: Error when extracting scout time series - #2 by Raymundo.Cassani
Please update Brainstorm and try again.
If you still get an error, there might be an issue during the update, or you may have multiple versions of Brainstorm in your Matlab path. For debugging this further, type edit panel_process_select in the Matlab command window, go to line 764, it should be:
import org.brainstorm.list.*;
Otherwise, you do not have the current version of Brainstorm on your computer. Delete the brainstorm3 folder, and download a new one from the website.