Background: Our JIRA Agile setup has a separate board for each team. Each team has their own project. There is one shared project that houses all the Epics.
Problem: There is one board cannot start a sprint and get the error "Error There can only be one active sprint on each board", but if they go to the "Active sprints" view the message "There are no active sprints." is displayed.
Theory: I think some stories were placed into sprints on one team's board and then moved to the other team's board, duplicating the same sprint ID across boards. Sprint handling has caused problems on several occasions. Most of the time in the UI, Sprint is treated as part of a Board, but the fact that Sprint is really just metadata on the issue allows for things to really get messed up.