From: Falkland Islands
This might be happening in the case of too litle space remaining after writing the first session.
It might also be the case of a new compilation based on a wizard, if your software permits this.
An extreme case is an old recorder unable to write multisession discs (quite rare, I think).
Last, it might be a case to be forced to choose track at once instead of sessson/disc at once during the disc preperation.
I hope I have helped you, rather than confused you...
WM # CI