I have Windows XP operating system...My problem is I am trying to burn a DVD using  .mkv files, but the subtitles are not showing up.
I read the guide posted here for using MKVetractGUI.exe, so downloaded it and extracted the subtitle track as a .ass file no problem. However when using ConvertXtoDVD I click to add the subtitle track and I get the message "Skipping subtitle file Reason: Empty or unsupported format. The .ass file are listed as a Substation Alpha V4+ under types of files. Any help on why this isn't working?
Update to this is, I also tried using Subtitle Workshop to save the file as a dvd subtitle file and I still get the same message regardless of what type of file I save it to.

Does Xilisoft DVD tools work on .mkv files, I don't see that listed as a supported format. It says to rip subtitles from DVDs and I am not working from a DVD. I also didn't see any other program on that site that listed mkv to DVD.