problem

It may happen randomly, that a user is not able to access a task after opening it.

The error message is then: You are not authorized to access the requested data.
Server Message: You don't have any task opened (anymore) for editing.

Reason

The problem comes from the session handling. It may happen that a HTTP request started before opening the task will be finished later after the task open call. That would remove the info about the opened task from the session.

Solution

The long term solution would be to remove this info from the session.

For now the session writing is changed, so that the session data is only overwritten if there is really a data change. This does not solve concurrent write processes, but the cases where session data really is changed are just rare. Mainly only login and task open / close.