I'm experiencing a problem with saving a target Excel file in SDL Trados Studio. I went through the other topics in the community but couldn't resolve the issue.

I'm running the latest product version. Here are the error details (I've only deleted the user and computer name an put ************** instead):

<SDLErrorDetails time="11-10-2019 15:29:43">
  <ErrorMessage>Failed to save target content: 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.FileTypeSupport.Filters.Excel</Source>
    <HResult>-2147467261</HResult>
    <StackTrace><![CDATA[   bij Sdl.FileTypeSupport.Filters.Excel.FilterControllerFramework.OfficeController.UpdateDocumentFile(XsltArgumentList argsList, XslCompiledTransform xslTransform, XPathNavigator child)
   bij Sdl.FileTypeSupport.Filters.Excel.FilterControllerFramework.OfficeController.IterateXsltFiles(XsltArgumentList argsList, FileMap rule, XPathNodeIterator iter, Boolean isUpdate, String targetFilePath)
   bij Sdl.FileTypeSupport.Filters.Excel.FilterControllerFramework.OfficeController.IterateContentType(String xslFileNamesPath, Boolean isUpdate, String filePath, String filterStr, String targetFilePath, Boolean isCalledByRelsTableIteration)
   bij Sdl.FileTypeSupport.Filters.Excel.FilterControllerFramework.OfficeController.serviceBackward()
   bij Sdl.FileTypeSupport.Filters.Excel.PlugInFilter.FileParser.DocumentParser.Update()
   bij Sdl.FileTypeSupport.Filters.Excel.PlugInFilter.FileParser.DocumentExtractImpl.Update(DocumentCollection srcCollection, String filename, String tgtFilePath)
   bij Sdl.FileTypeSupport.Filters.Excel.PlugInFilter.FileWriterAndPreviewFileWriter.WriterImpl.EndOfInput()
   bij Sdl.FileTypeSupport.Filters.Excel.PlugInFilter.FileWriterAndPreviewFileWriter.ExcelWriter.EndOfInput()
   bij Sdl.FileTypeSupport.Framework.Integration.NativeWriterMessagesProxy.EndOfInput()
   bij Sdl.FileTypeSupport.Framework.Integration.FileGenerator.CallEndOfInput()
   bij Sdl.FileTypeSupport.Framework.Integration.FileGenerator.FileComplete()
   bij Sdl.FileTypeSupport.Framework.Integration.AbstractBilingualProcessorContainer.FileComplete()
   bij Sdl.FileTypeSupport.Framework.Integration.MultiFileConverter.FileComplete()
   bij Sdl.FileTypeSupport.Framework.BilingualApi.AbstractBilingualContentProcessor.FileComplete()
   bij Sdl.FileTypeSupport.Framework.Integration.AbstractBilingualProcessorContainer.FileComplete()
   bij Sdl.FileTypeSupport.Bilingual.Tmfc.TmfcReaderImpl.vv_Visit(TmfcReaderImpl* , FrameworkFileContainerField* field)
   bij FrameworkFileContainerField.vv_AcceptFrameworkVisitor(FrameworkFileContainerField* , FrameworkFieldVisitor* visitor)
   bij Sdl.FileTypeSupport.Bilingual.Tmfc.TmfcReaderImpl.vv_VisitStartEndField(TmfcReaderImpl* , StartEndField* startEnd)
   bij Sdl.FileTypeSupport.Bilingual.Tmfc.TmfcReaderImpl.b_VisitNext(TmfcReaderImpl* )
   bij Sdl.FileTypeSupport.Bilingual.Tmfc.TmfcReader.ParseNext()
   bij Sdl.FileTypeSupport.Framework.Integration.FileExtractor.ParseNext()
   bij Sdl.FileTypeSupport.Framework.Integration.MultiFileConverter.ParseNext()
   bij Sdl.FileTypeSupport.Framework.Integration.MultiFileConverter.Parse()
   bij Sdl.TranslationStudio.Editor.TranslationEditor.TranslatableDocument.SaveMonolingualAsJobRequest.Execute(IJobExecutionContext context)
   bij Sdl.Desktop.Platform.Implementation.Services.Job.<_worker_DoWork>b__46_0()
   bij Sdl.Desktop.Platform.Implementation.Services.Log.Resources(Object message, Action action)
   bij Sdl.Desktop.Platform.Implementation.Services.Job._worker_DoWork(Object sender, DoWorkEventArgs e)
   bij System.ComponentModel.BackgroundWorker.OnDoWork(DoWorkEventArgs e)
   bij System.ComponentModel.BackgroundWorker.WorkerThreadStart(Object argument)]]></StackTrace>
  </Exception>
  <Environment>
    <ProductName>SDL Trados Studio</ProductName>
    <ProductVersion>14.0.0.0</ProductVersion>
    <EntryAssemblyFileVersion>14.1.10017.54688</EntryAssemblyFileVersion>
    <OperatingSystem>Microsoft Windows 10 Home</OperatingSystem>
    <ServicePack>NULL</ServicePack>
    <OperatingSystemLanguage>1043</OperatingSystemLanguage>
    <CodePage>1252</CodePage>
    <LoggedOnUser> ************** </LoggedOnUser>
    <DotNetFrameWork>4.0.30319.42000</DotNetFrameWork>
    <ComputerName> ************** </ComputerName>
    <ConnectedToNetwork>True</ConnectedToNetwork>
    <PhysicalMemory>8350604 MB</PhysicalMemory>
  </Environment>
</SDLErrorDetails>

Does anyone know what is causing the problem based on the error details?