Crystal Server sessions do not log off

We have installed a trial version of Crystal Server. When we launch a report, we use something like this:

http://servername:8080/BOE/CMC/1606020932/CrystalReports/viewrpt.cwr?id=7122&apsuser=erp_viewer&apspassword=password

The report runs okay. But there is no way to log off the sessions. Even when we close the browser. So we run out of concurrent licenses very quickly.

The only option is either to reboot the server or wait the sessions to time out (which is about 20 minutes). Is there a way to resolve the issue? We are using Crystal Server 2013 SP1 (BI Platform 4.1 SP1).

Thanks