You have created a custom XML filter for a file that contains CDATA with HTML code, and used the option Process embedded content > Inside CDATA element with > HTML Embedded Content 5 2.0.0.0, but when trying to Preview the file, or open it in Trados for translation, you get the error:

Unable to open the input file for translation. Invalid syntax found at line: x, column: xy

 

<SDLErrorDetails time="2/14/2022 4:51:44 PM">
  <ErrorMessage>Unable to open the input file for translation. Invalid syntax found at line: 9, column: 26.</ErrorMessage>
  <Exception>
    <Type>Sdl.FileTypeSupport.Framework.FileTypeSupportException, Sdl.FileTypeSupport.Framework.Core, Version=1.0.0.0, Culture=neutral, PublicKeyToken=c28cdb26c445c888</Type>
    <HelpLink />
    <Source>Sdl.FileTypeSupport.Filters.Html</Source>
    <HResult>-2146233088</HResult>
    <StackTrace><![CDATA[   at Sdl.FileTypeSupport.Filters.Html.HtmlParserImpl.HtmlParser.ReadStartOrEmptyTag()
   at Sdl.FileTypeSupport.Filters.Html.HtmlParserImpl.HtmlParser.ParseEntity()
   at Sdl.FileTypeSupport.Filters.Html.Services.ParserService.Parse()
   at Sdl.FileTypeSupport.Filters.Html.Parser.ParseNext()
   at Sdl.FileTypeSupport.Framework.Integration.SubContentExtractor.ParseNext()
   at Sdl.FileTypeSupport.Framework.Integration.FileExtractor.PublisherProcessSubContent(Object sender, ProcessSubContentEventArgs args)
   at Sdl.FileTypeSupport.Filters.Xml.XmlParser.PublishContent(ProcessSubContentEventArgs eventArgs)
   at Sdl.FileTypeSupport.Filters.Xml.Core.EmbeddedContent.SubContentPublisher.PublishSubContent(Stream subContentStream, String embeddedContentTypeFromSettings)
   at Sdl.FileTypeSupport.Filters.Xml.Core.EmbeddedContent.SubContentPublisher.PublishEmbeddedSubContent(String content, String processorId)
   at Sdl.FileTypeSupport.Filters.Xml.Core.EmbeddedContent.SubContentPublisherWithStructureParagraph.SendContentToProcessor(String embeddedContentProcessorId)
   at Sdl.FileTypeSupport.Filters.Xml.Core.Parser.CdataConsumer.SendContentToSubcontentProcessor()
   at Sdl.FileTypeSupport.Filters.Xml.Core.Parser.CdataConsumer.OutputCdata(CdataNode cdata, ParserRuleMatchResult parentParserRuleMatchResult)
   at Sdl.FileTypeSupport.Filters.Xml.Core.Parser.CdataConsumer.HandleCdataInsideStructureRule(CdataNode cdata, ParserRuleMatchResult parentParserRuleMatchResult)
   at Sdl.FileTypeSupport.Filters.Xml.Core.Parser.CdataConsumer.Consume(XmlNodeMessage`1 message)
   at Sdl.FileTypeSupport.Filters.Xml.Core.Messaging.Consumer`1.TryConsume(IMessage message)
   at Sdl.FileTypeSupport.Filters.Xml.Core.Messaging.InMemoryMessageBus.Publish(IMessage message)
   at Sdl.FileTypeSupport.Filters.Xml.Core.Messaging.MessagePublisher.PublishXmlNodeMessage[T](T node)
   at Sdl.FileTypeSupport.Filters.Xml.Core.XmlNodes.XmlNodesDispatcher.ReadAndDispatchNodes()
   at Sdl.FileTypeSupport.Filters.Xml.XmlParser.ReadAndDispatchXmlNodes(Stream inputStream, Encoding fileEncoding)
   at Sdl.FileTypeSupport.Filters.Xml.XmlParser.ParseNext()
   at Sdl.FileTypeSupport.Framework.Integration.FileExtractor.ParseNext()
   at Sdl.FileTypeSupport.Framework.Integration.MultiFileConverter.ParseNext()
   at Sdl.FileTypeSupport.Framework.Integration.MultiFileConverter.Parse()
   at Sdl.TranslationStudio.Editor.TranslationEditor.TranslatableDocument.Load(IJobExecutionContext context)
   at Sdl.Desktop.Platform.Services.JobRequest.Execute(IJobExecutionContext context)
   at Sdl.Desktop.Platform.Implementation.Services.JobExecuter.Execute(JobData jobData)
   at Sdl.Desktop.Platform.Implementation.ResourceLoggingInternalCommandExecuter`1.ExecuteWithResourceLogging(TCommandData commandData, String message)
   at Sdl.Desktop.Platform.Implementation.Services.Job._worker_DoWork(Object sender, DoWorkEventArgs e)
   at System.ComponentModel.BackgroundWorker.OnDoWork(DoWorkEventArgs e)
   at System.ComponentModel.BackgroundWorker.WorkerThreadStart(Object argument)]]></StackTrace>
  </Exception>

 

There are several workarounds:
- Try to check the HTML code in the CDATA section of the source file for doubled angled brackets or other issues.
- When HTML embedded content processor is used, content must be "valid" HTML. In this case, characters like < and > must be escaped as an entity, for example, &lt; instead of < ,  https://www.w3schools.com/html/html_entities.asp
- Use another embedded content processor in Trados - e.g. Plain text embedded content processor
- Define regex rules to process the content

HMTL code in CDATA is invalid and Trados cannot process it.
There are doubled angle brackets for the tags e.g. << >>, or < <  > > or other variations, or incorrectly closed tag pairs or tags.If you use the less than (<) or greater than (>) signs in your text, the browser might mix them with tags. 
If you use the less than (<) or greater than (>) signs in your text, the browser might mix them with tags.