If you are unable to open a new review because of this error, this indicates that a current review is still outstanding.
To close the cycle of a review, you will need to close the review for all employees who were involved in the first cycle.
Then you will need to change the Completion Date to a future date to run the new cycle.
To know who has the review open you will need to run a query on the following fields:
Performance Name.
Performance Start Date.
Employee Performance Status.
Manager Performance Status.
📌Note: As long as there is an employee or manager who has not closed the review, the review will still be considered open. Thus, no one can start a new cycle.