I actually have this  problem when a try to save terms to the termbase. It's a large project on which I've been working for 2 weeks. It's the 1st time  I have this problem with this particular project.
Details:
<?xml version="1.0"?>

-<SDLErrorDetails time="9-10-2017 11:46:20">

<ErrorMessage>De objectverwijzing is niet op een exemplaar van een object ingesteld.</ErrorMessage>


-<Exception>

<Type>System.NullReferenceException, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</Type>

<HelpLink/>

<Source>Sdl.MultiTerm.Core.Common</Source>

<HResult>-2147467261</HResult>


-<StackTrace>

-<![CDATA[ bij Sdl.MultiTerm.Core.Common.DataContainers.TermbaseStatus..ctor(ITermbaseInfo info)
bij Sdl.MultiTerm.Client.MiniEditor.MiniEditorControl..ctor(ITermbaseInfo activeTermbase, ITermHit activeTerm)
bij Sdl.TranslationStudio.Editor.Terminology.TermbaseViewer.MultiTermViewerWinFormsUI.AddTerm(ITermbaseInfo termbaseInfo, String source, String target)
bij Sdl.TranslationStudio.Editor.Terminology.TermbaseViewer.MultiTermViewerWinFormsUI.AddTerm(String source, String target)
bij Sdl.TranslationStudio.Editor.Terminology.TermbaseViewer.TermBaseViewPartX.TerminologyProviderViewerAddTerm(String source, String target)
bij Sdl.TranslationStudio.Editor.Terminology.TermbaseViewer.TermBaseViewPartX.AddTerm(ITerminologyProvider termbase, String source, String target)
bij Sdl.TranslationStudio.Editor.Terminology.Actions.AbstractAddNewTermAction.AddTerm()
bij Sdl.TranslationStudio.Editor.Terminology.Actions.QuickAddNewTerm.Execute()
bij Sdl.Desktop.Platform.Implementation.CommandBars.StaticAction.Execute()
bij Sdl.Desktop.Platform.Implementation.CommandBars.ActionService.<>c__DisplayClass3.<ExecuteAction>b__2()
bij Sdl.Desktop.Platform.Implementation.Services.Log.Resources(Object message, Action action)
bij Sdl.Desktop.Platform.Implementation.CommandBars.ActionService.ExecuteAction(IAction action, ActionOrigin origin, Boolean allowToggle)
bij Sdl.Desktop.Platform.WinForms.IgCommandBarAction.Execute()
bij Sdl.Desktop.Platform.WinForms.IgCommandBarAction._lazyButtonTool_ToolClick(Object sender, ToolClickEventArgs e)
bij Infragistics.Win.UltraWinToolbars.ToolBase.OnToolClick(ToolClickEventArgs e)
bij Infragistics.Win.UltraWinToolbars.UltraToolbarsManager.OnToolClick(ToolClickEventArgs e)
bij Infragistics.Win.UltraWinToolbars.UltraToolbarsManager.FireEvent(ToolbarEventIds id, EventArgs e)
bij Infragistics.Win.UltraWinToolbars.ToolBase.OnToolClick()
bij Infragistics.Win.UltraWinToolbars.ButtonToolUIElement.DoClickProcessing(MouseEventArgs e)
bij Infragistics.Win.UltraWinToolbars.ButtonToolUIElement.OnMouseUp(MouseEventArgs e)
bij Infragistics.Win.ControlUIElementBase.ProcessMouseUpHelper(Object sender, MouseEventArgs e)
bij Infragistics.Win.ControlUIElementBase.ProcessMouseUp(Object sender, MouseEventArgs e)
bij Infragistics.Win.Utilities.ProcessEvent(Control control, ProcessEvent eventToProcess, EventArgs e)
bij Infragistics.Win.UltraWinToolbars.UltraToolbarsDockArea.OnMouseUp(MouseEventArgs e)
bij System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
bij System.Windows.Forms.Control.WndProc(Message& m)
bij System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
bij System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
bij System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)]]>
</StackTrace>

</Exception>


-<Environment>

<ProductName>SDL Trados Studio</ProductName>

<ProductVersion>12.0.0.0</ProductVersion>

<EntryAssemblyFileVersion>12.3.5281.10</EntryAssemblyFileVersion>

<OperatingSystem>Microsoft Windows 10 Home</OperatingSystem>

<ServicePack>NULL</ServicePack>

<OperatingSystemLanguage>1043</OperatingSystemLanguage>

<CodePage>1252</CodePage>

<LoggedOnUser>LAPTOP-LIEVE\Lieve</LoggedOnUser>

<DotNetFrameWork>4.0.30319.42000</DotNetFrameWork>

<ComputerName>LAPTOP-LIEVE</ComputerName>

<ConnectedToNetwork>True</ConnectedToNetwork>

<PhysicalMemory>6138604 MB</PhysicalMemory>

</Environment>

</SDLErrorDetails>