Nero dvd burning, disabled?

[Remyisme]

I've tryed to burn a data DVD through Nero Express on Nero 7. And I already had a compilation and I pressed on the BURN button, but than I immideatley remembered that, I forgot to select the desirable writing speed, so I clicked on ABORT button, and it was aborted really before it started, so I selected the speed, and than tryed to burn it again, but it didn't let me. It says somehow, that the disc-at-once option is disabled. And I went back to the adding videos box, and you know this, red line there that indicates, the size up to which you can still add the files to your compilation?
So it disappeared, and instead it became yellow, and I know I need it red, and I can't get it back now, I've looked in options, and I can't see what to do to make it the way it was, please help anyone who knows.

[TBoneit]

Change the disc, you started the burn and then aborted it, that's it for that disc.

[Remyisme]

I did change it, but it is still so, I inserted a new disc, but as I open Nero, the line is yellow, and not red.

[Remyisme]

I sucsseded to, record a disc, but without the disc-at-once option, can anyone say, if it's gonna hurt the disc in future? I checked the recorded disc, and it works, will there be a problem in future?