"Could not store session XML" can be seen in a variety of situations, but it is most commonly seen when there is too little disk space on the server to store data for the submitted session. To verify, look at the server's logs, which are stored by default in C:\mfs\logs, but may have been configured to be stored elsewhere. It is possible that you may not have sufficient permissions to view the logs — if this is the case, someone else in your organization does; contact them to obtain a copy of the logs. If the logs are not sufficient to diagnose the issue, contact Mi-Co support, and include a copy of the logs in your message.