There are many sub formats. Are you sure that the one you ripped was in.srt format or if it was another one which was unrecognised(propreitary) by the srt2sup utility. That could be one reason for the green box OR it did you check the box "Rip Subtitles" in the DVD2SVCD tab for that specific purpose. Did you check the .srt file itself, whether it is proper. There are many sub utils which allow preview for this specific purpose. OR could be None of the above and something else.
Hope this helps.