I tried to add subtitle file (.sub) using Avi2Svcd to convert an avi to mpeg file, but got an error message : "list index out of bounds".

Had never had that happened before. I still have the .idx and .sub file but have no idea how to edit either or both of these if this is necessary. I also have no idea if there is an utility to correct the files.
Any help certainly appreciated.

Convert the *.IDX file to *.srt subtile file using VobSub (well, actally its Subresync program) Load in the *.idx, hit Save As and select *.srt format [the top one], it will then do a ocr conversion to text format. Load the new *.srt into dvd2svcd and it will now work fine.

Hi ChickenMan. Thanks for your quick reply. Subresync comes up with a box saying "Add matching letter" with the highlighted letter/letters on the side and beneath. I tried matching but seems it goes on and on. Thought I'd ask if you know what's wrong here before continuing matching all if necessary. Hope you're having a nice evening.

Yep, thats what it should do, its doing an OCR (Optical Character Recognition) where its trying to convert the graphics imahages to text. It will generally find all lowercase, upercase and a the few commars, full stops, quotes, etc. Doesnt take long really. Just match them up.

Thank you ChickenMan. Everything worked fine! Appreciate your help very much. I'll check the link you provided. Have a nice day