Using Studio 2015 and translated an Excel file over several days. When I tried to generate the target translation, I received 2 error messages.

1st message:

Object reference not set to an instance of an object.
Origin: Sdl.FileTypeSupport.Filters.Excel.PlugInFilter.FileWriterAndPreviewFileWriter.ExcelWriter

2nd message:

Object reference not set to an instance of an object.
Origin: Generate Target Translations

I tried several solutions suggested in the past. First I used the same source file and created a new, single-document project, used the TM to translate. Same results. Second, I resolved all the tag errors and attempted to generate target. Same results. I thought about saving the source XLSX file as XLS, but the source file's integrity cannot be maintained, so I abandoned that idea.

Here is the detailed error message:

<SDLErrorDetails time="9/14/2018 4:44:27 PM">
<ErrorMessage>Object reference not set to an instance of an object.</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[ at Sdl.FileTypeSupport.Filters.Excel.FilterControllerFramework.OfficeController.UpdateDocumentFile(XsltArgumentList argsList, XslCompiledTransform xslTransform, XPathNavigator child)
at Sdl.FileTypeSupport.Filters.Excel.FilterControllerFramework.OfficeController.IterateXsltFiles(XsltArgumentList argsList, FileMap rule, XPathNodeIterator iter, Boolean isUpdate, String targetFilePath)
at Sdl.FileTypeSupport.Filters.Excel.FilterControllerFramework.OfficeController.IterateContentType(String xslFileNamesPath, Boolean isUpdate, String filePath, String filterStr, String targetFilePath, Boolean isCalledByRelsTableIteration)
at Sdl.FileTypeSupport.Filters.Excel.FilterControllerFramework.OfficeController.serviceBackward()
at Sdl.FileTypeSupport.Filters.Excel.PlugInFilter.FileParser.DocumentParser.Update()
at Sdl.FileTypeSupport.Filters.Excel.PlugInFilter.FileParser.DocumentExtractImpl.Update(DocumentCollection srcCollection, String filename, String tgtFilePath)
at Sdl.FileTypeSupport.Filters.Excel.PlugInFilter.FileWriterAndPreviewFileWriter.WriterImpl.EndOfInput()
at Sdl.FileTypeSupport.Filters.Excel.PlugInFilter.FileWriterAndPreviewFileWriter.ExcelWriter.EndOfInput()
at Sdl.FileTypeSupport.Framework.Integration.NativeWriterMessagesProxy.EndOfInput()
at Sdl.FileTypeSupport.Framework.Integration.FileGenerator.CallEndOfInput()
at Sdl.FileTypeSupport.Framework.Integration.FileGenerator.FileComplete()
at Sdl.FileTypeSupport.Framework.BilingualApi.AbstractBilingualContentProcessor.FileComplete()
at Sdl.FileTypeSupport.Framework.Integration.AbstractBilingualProcessorContainer.FileComplete()
at Sdl.FileTypeSupport.Framework.Integration.MultiFileConverter.FileComplete()
at Sdl.FileTypeSupport.Framework.BilingualApi.AbstractBilingualContentProcessor.FileComplete()
at Sdl.FileTypeSupport.Framework.Integration.AbstractBilingualProcessorContainer.FileComplete()
at Sdl.FileTypeSupport.Bilingual.SdlXliff.XliffFileReader.OnEndFile()
at Sdl.FileTypeSupport.Bilingual.SdlXliff.SdlXliffFeeder.<ContinueScanning>b__2(ISdlXliffStreamContentHandler handler)
at System.Collections.Generic.List`1.ForEach(Action`1 action)
at Sdl.FileTypeSupport.Bilingual.SdlXliff.SdlXliffFeeder.ContinueScanning()
at Sdl.FileTypeSupport.Bilingual.SdlXliff.XliffFileReader.ContinueParsing()
at Sdl.FileTypeSupport.Bilingual.SdlXliff.XliffFileReader.ParseNext()
at Sdl.FileTypeSupport.Framework.Integration.FileExtractor.ParseNext()
at Sdl.FileTypeSupport.Framework.Integration.MultiFileConverter.ParseNext()
at Sdl.FileTypeSupport.Framework.Integration.MultiFileConverter.Parse()
at Sdl.ProjectApi.AutomaticTasks.NativeFileGenerator.GenerateFiles(ContentRestriction restriction, Boolean preview, Int32 filePercentBase, Int32 filePercentFactor)
at Sdl.ProjectApi.AutomaticTasks.GenerateTargetTranslation.GenerateTargetTranslationTask.ProcessFile(IExecutingTaskFile executingTaskFile)
at Sdl.ProjectApi.AutomaticTasks.AbstractFileLevelAutomaticTaskImplementation.Execute()]]></StackTrace>
</Exception>
<Environment>
<ProductName>SDL Trados Studio</ProductName>
<ProductVersion>12.0.0.0</ProductVersion>
<EntryAssemblyFileVersion>12.3.5281.10</EntryAssemblyFileVersion>
<OperatingSystem>Microsoft Windows 7 Ultimate </OperatingSystem>
<ServicePack>Service Pack 1</ServicePack>
<OperatingSystemLanguage>1033</OperatingSystemLanguage>
<CodePage>932</CodePage>
<LoggedOnUser>Hajime-PC\Hajime</LoggedOnUser>
<DotNetFrameWork>4.0.30319.42000</DotNetFrameWork>
<ComputerName>HAJIME-PC</ComputerName>
<ConnectedToNetwork>True</ConnectedToNetwork>
<PhysicalMemory>16754160 MB</PhysicalMemory>
</Environment>
</SDLErrorDetails>

I hope someone can offer a solution. There is a lot of data and I don't want to copy-and-paste translated text to hundreds of cells manually. Thanks in advance.