error moving around members in a hierarchy

hi all -- in MDS 2012,  I am trying to move around members in Explorer (under different parents in an hierarchy) and get the following error, that does not seem to be very descriptive  -- does anyone have any background on it and how it can be mitigated?  

thx a big bunch,

Cos

System.NullReferenceException: [Arg_NullReferenceException]

Arguments:

Debugging resource strings are unavailable. Often the key and arguments provide sufficient information to diagnose the problem. See http://go.microsoft.com/fwlink/?linkid=106663&Version=5.1.30514.00&File=mscorlib.dll&Key=Arg_NullReferenceException

   at Microsoft.MasterDataServices.Client.View.UserControls.EntityMembersDataForm.IsCurrentMemberReadonly()

   at Microsoft.MasterDataServices.Client.View.UserControls.EntityMembersDataForm.UpdateStaticFields()

   at Microsoft.MasterDataServices.Client.View.UserControls.EntityMembersDataForm.MemberDataForm_ContentLoaded(Object sender, DataFormContentLoadEventArgs e)

   at System.Windows.Controls.DataForm.OnContentLoaded(DataFormContentLoadEventArgs e)

   at System.Windows.Controls.DataForm.OnContentRootElementLoaded(Object sender, RoutedEventArgs e)

   at MS.Internal.CoreInvokeHandler.InvokeEventHandler(UInt32 typeIndex, Delegate handlerDelegate, Object sender, Object args)

   at MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex, Int32 actualArgsTypeIndex, String eventName, UInt32 flags)