SUB TO SRT subtitle help!

I want to convert sub to srt. Which program should i use to conver them cause subtitles are in two different video files. I am using Divx to DVd guide by chickenman but when i try to select the *.sub file error comes up saying list index out of bound (0). I don’ know what is going on i thought converting them to srt will solve the problem. If you have any suggestions please help.