The IIS Application pool Recycling was not configured or is miss-configured . Without this configured IIS will continue to use memory for the web application until its allotted memory is full. It will then recycle to clear the memory. This happens all existing session are terminated. Since DRM work primarily in memory all data not saved to the database will be lost.
To configure this parameter follow these steps:
To open IIS Manager from the Start menu
Click System and Security, and then click Administrative Tools.
In the Administrative Tools window, double-click Internet Information Services (IIS) Manager.
To open IIS Manager from the Search box
In the Start Search box, type inetmgr and press ENTER.
In the Connections pane, expand the server node
Click Application Pools.
On the Application Pools page, select an application pool generally drm_pool,
Click Recycling in the Actions pane
Click the box next to Specific time
In the box below enter a non business time ( IE 2:30 AM)
Click Recycle on the right hand side ( this will activate the changes)
Close IIS Manager