Please note that the HIT link will become inactive (casuing Workers to be unable to take your HIT) under a few conditions
1. if the HIT is not Live (expired, stopped), OR
2. Changes were made to the HIT which causes the link to get invalidated
3. The HIT was stopped or completed
If you make any changes to the study (like price, qualifications, etc) after sending it out that will also invalidate the HIT link and workers will receive a message that the HIT is not available.