When I open an avi file and in its properties I click on subtitles I get access violation error 2 times. The subtitle file was .sub.
I renamed it to .srt and ConvertXtoDVD opened it just fine.

ConvertXtoDVD supports .sub/.idx pair format and .srt format (text only).
Just .sub without .idx is different format and is not supported (yet?).

hmm, when I renamed .sub to .srt I played it on my pc ->avi + sub but when I convert it with ConvertXtoDVD to a DVD my DVD player says that there are no subtitles. This is strange. Maybe when I only rename .sub to .srt I can play it on my pc but to play it in my DVD I must convert .sub to .srt completely not just rename it.

download vobsub and use the subresync tool in it to fix up all your sub problems. it can convert from microdvd(.sub) to subripper(.srt) and also .sub+.idx to .srt which is useful if you want to change frame rates as sub/idx is limited to the original movies framerate.

also subtitle workshop is a pretty good alternative as well

media players on the pc are very lenient when it comes to subtitles, renaming doesnt work, if the file format in the actual subtitle file is different. convertxtodvd is more stricter so try and use .srt where ever possible as its the most flexible. if you are doing pal->pal or ntsc->ntsc sub/idx are fine

Thank you. I am using subtitle workshop - it is very good. I will know from now on that I need to convert all my subtitle files to .srt and everything should work fine. The thing that misled me was that the movie was played with the renamed .sub as .srt fine on my pc and I thought that it will be ok with ConvertXtoDVD too. When I load the movie in ConvertXtoDVD it opened and recognized the renamed .sub as .srt file but I couldn't get the properties for the subtitle file (font,size..) and after I burn it, the subtitles doesn't work. I will know from now on that I must use real proper .srt file with ConvertXtoDVD.
I will try vobsub.
Thanks for the help.