If Toast said there were errors on the disc, that means there were errors on the disc. Usually, this happens because you are burning too fast (use a slower burn speed in Toast), or because you are using a bad brand of blank CD.
There is a BIG difference between different brands of blank CD! TDK and Verbatim are among the best, memorex among the worst.
A CD, once it is recorded, will *always* show 0K available. It makes no difference if you fill ed the CD or not.
If you want to add more to a CD later, you must record it using the Toast "Write Session" button, not the "Write Disc" button. It will still show zero K free; you use Toast to record more information, which will appear on your desktop as a second CD (that is, you will insert the CD and TWO icons will show up--one for the first session and one for the second session).