Candidate can login to exam from one location/ browser window. In case candidate tries to login using same credentials at 2 different locations or 2 different browsers then system would show as error message as ” Your previous session is already active!”
Admin can re enable session for the candidate from admin section as shown below.
Go to Candidates > Candidate Data and select candidate to clear session.
In this case if candidate logs in for the online exam and closes examination window then previous session of the candidate should be cleared in order to start online examination for the candidate.