If you place the media you atttempted to create back in the Recorder, and launch Nero and go to Recorder->Medium Info. And from this window select the last session on the CD. And in the bottome left of the window you should see two options for Close Session or Close Disc.
Choose Close session of you wish to write to the CD again, or close disc if you have no plans to write to the CD ever again.
Are you then able to read the data you had written to the CD?