MultiTerm 2017 issue

I have been working smoothly with MultiTerm in conjunction with Studio 2017 for around 6 months, but today there seems to be a block in adding new terms from the Studio editing window. When I try to add a new term, a term I added earlier today appears in the MultiTerm add popup window. A message appears indicating that the new term has been added, but none of the entries since that earlier term have actually been added.

<?xml version="1.0"?>
-<SDLErrorDetails time="7/15/2017 2:21:48 PM">
<ErrorMessage>An item with the same key has already been added.</ErrorMessage>
-<Exception>
<Type>System.ArgumentException, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</Type>
<ParamName/>
<HelpLink/>
<Source>mscorlib</Source>
<HResult>-2147024809</HResult>
-<StackTrace>
-<![CDATA[ at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
at Sdl.TranslationStudio.Editor.Terminology.TermbaseViewer.ProviderTermbasesChange.Subscribe(ITranslatableDocument doc, Action`1 action)
at Sdl.TranslationStudio.Editor.Terminology.EditorTermbaseMandatoryFieldCheck.HasMandatoryFields(ITranslatableDocument document)
at Sdl.TranslationStudio.Editor.Terminology.Actions.Conditions.QuickAddNewTermCondition.GetValue()
at Sdl.Desktop.Platform.Extensions.AbstractCondition.UpdateValue()
at Sdl.TranslationStudio.Editor.Terminology.Actions.Conditions.SourceTermSelectedForAddition.SelectionChanged(Object sender, SelectionChangedEventArgs e)
at System.EventHandler`1.Invoke(Object sender, TEventArgs e)
at AbstractFrameworkEditControl.raise_SelectionChanged(Object value0, SelectionChangedEventArgs value1)
at FrameworkEditControl.OnSelectionChanged(Object sender, SelectionChangedEventArgs args)
at FrameworkEditControlEventSource.SelectionChanged(FrameworkEditControlEventSource* )
at Tree.DocumentControl.vl_WindowProc(DocumentControl* , HWND__* , UInt32 , UInt32 , Int32 )
at FrameworkDocumentControl.vl_WindowProc(FrameworkDocumentControl* , HWND__* h_wnd, UInt32 n_msg, UInt32 w_p, Int32 l_p)
at System.Windows.Forms.UnsafeNativeMethods.CallWindowProc(IntPtr wndProc, IntPtr hWnd, Int32 msg, IntPtr wParam, IntPtr lParam)
at System.Windows.Forms.NativeWindow.DefWndProc(Message& m)
at System.Windows.Forms.Control.DefWndProc(Message& m)
at System.Windows.Forms.Control.WmMouseMove(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)]]>
</StackTrace>
</Exception>
-<Environment>
<ProductName>SDL Trados Studio</ProductName>
<ProductVersion>14.0.0.0</ProductVersion>
<EntryAssemblyFileVersion>14.0.5889.5</EntryAssemblyFileVersion>
<OperatingSystem>Microsoft Windows 10 Home</OperatingSystem>
<ServicePack>NULL</ServicePack>
<OperatingSystemLanguage>1033</OperatingSystemLanguage>
<CodePage>1252</CodePage>
<LoggedOnUser>VAIO\Simon</LoggedOnUser>
<DotNetFrameWork>4.0.30319.42000</DotNetFrameWork>
<ComputerName>VAIO</ComputerName>
<ConnectedToNetwork>True</ConnectedToNetwork>
<PhysicalMemory>8334620 MB</PhysicalMemory>
</Environment>
</SDLErrorDetails>

Does anyone know how I can resolve this?

Many thanks in advance, Simon