Convert/Open a closed CD-r to be written again?

Hi, Im a newbie. My os is xp, using nero burn express 6.0. I had a new 700mb CD-R & put only one 2mb file on it. I was trying to add more files to it later, but kept getting errors that cd was read-only & needed a write CD. I checked the disc info & it did state so, then I even tried to erase the disc, but wasnt allowed. How can I re-open or convert this newly used cd-r to be written onto again? or is it a lost cause? After further going thru Neros help topics & menus and then to the detailed final burn settings under the More settings (you have to click to open more detailed settings) I did see a check box under the "Write Method" for "Finalized Disc" which apparently was checked. This was the 1st time I had ever seen this & it must of been what happened to this burn (Note: I also have another cd-r disc that was burned previous to this one in question & I reviewed it & it to is a read-only, I still wanted to put more files on that one as well ). I now have unchecked the Finalized Disc option. I'd appreciate any advice if this can be fixed. Thnx

 

Have you noticed that there are different burn sessions like 'Start Multi Session' & 'Continue Multi' & No Multi or words to that effect .. also just before you press burn there should also be an option there that says 'Allow Files to be added later (Multisession) If you have NOT chosen Multi Session the next time you go to add some more data it will NOT be possible.