Hello,
I'm trying to add a 500Meg folder to a DL DVD.
For a stupid reason (hurry, urgent), I previously burned a 721Meg iso (from a cd) to that DVD but I'm pretty sure I checked the ability to have multi-sessions.
Now when I try to add data, it begins the operation but Nero shuts down after 5 seconds. Pouf ! I do choose "continue Multi-session disc" and tried "Refresh compilation when importing session", same result. No error message, no warning, and I can't find a log.
If anybody could tell me that "it's just not possible after burning an iso", or give me obvious the little trick I missed, I'd be delighted.

I think when you burned the iso image it probably closed the disc, meaning single session; thus it would not be possible to 'convert' it into a multisession disc afterwards.

It probably burned using DAO or disc-at-once, again this closes the disc.

Usually multisession is used when burning a data disc and must be specified in the beginning.

You could probably scan the disc using imgburn or dvdinfo to verify this.