This option re-opens a Questionnaire that has been closed, in order to allow further responses (often because an important responder missed the response deadline).
Explanation: A Questionnaire is closed to further responses whenever a Subject's Report is generated. The reason is that allowing additional responses would make the existing Report no longer correct.
Other events that will close a Questionnaire are: Generating a Group Report, Export, or a Report for another Subject that includes this current Subject's ratings as part of a group comparison.
Re-open closed questionnaires on the PEOPLE tab by selecting the Subject(s) whose Questionnaire you wish to re-open. Then, click the "More Actions" dropdown and select "Re-open Closed Questionnaires".