"do not convert audio" greyed out

[spliffman]

I have been using dvd2svcd to recode a film to fit on one DVD-R with excellent results, however one thing really bugs me the "do not convert audio" is greyed out so I cant select it. I can still use the original ac3 but the size of the film is usually just a little too big if I leave the disk size on 4200 on the bitrate tab, I guess this is because it recodes the film to a size to allow for the converted audio not the original ac3, so i am having to make an educated guess at the disk size.
More of an annoyance than a major problem but it is really bugging me.
Using build 1c of dvd2svcd, any help appreciated.

Thanks

[dvd2svcd]

select "No Images" in the CD image tab.

[spliffman]

As easy as that.....
Many thanks