Some time cockpit beta users reported problems when viewing projects or timesheets in the administration module. The following exception occured when they tried to open a list of projects or timesheets:

Object reference not set to an instance of an object.

   at System.Windows.Automation.Peers.AutomationPeer.EnsureChildren()
   at System.Windows.Automation.Peers.AutomationPeer.UpdateChildrenInternal(Int32 invalidateLimit)
   at System.Windows.Automation.Peers.AutomationPeer.UpdateChildren()
   ...

Finally we found out that this exception was caused by a windows service named "Tablet PC Input Service" and it is unique to entities that contain date and time fields. Stopping this service solves the problem.

Find more information under http://connect.microsoft.com/VisualStudio/feedback/details/316681/nullreferenceexception-in-system-windows-automation-peers-groupitemautomationpeer-getchildrencore.

Workaround

To resolve this problem stop the "Tablet PC Input Service".