Error in Edit Pending Worker

Summary: Error in Edit Pending Worker

Content (required): Hi All,

We have a Requisition in which 4 candidates were taken into consideration, out of 2 are now hired, one is currently pending worker. And one was 'Rejected By Employer' after drafting offer but was not converted to Pending Worker.

Now the Position has Headcount and FTE as 3, 2 active employees are already there. But when the On Boarding team is trying to edit the pending worker(changing email id) they are getting error as 'You can't select this position because it doesn't have an open headcount'. 

Please suggest why this error is coming. Ideally the fourth candidate was never converted to pending worker. He was rejected by employer.