problem writing cd's

[Gerard Tripptree]

I have a 700MHz, dual USB iBook with the the Toshiba DVD ROM SD-R2002 
that is giving me problems when I attempt to write out new cd-r's or 
cd-rw's.

Previously, I had no problem writing or adding additional sessions to 
CD'S until the disk was full. I used either Toast Titanium or the 
Apple CD writer. Lately, I have only been able to write ONE session 
to a CD or cd-rw. It does not matter how much free space remains on 
the disk, I cannot add any more sessions to the disk. This happens 
with both Toast and the Apple CD writer.

Toast appears to over-write the existing session with the new one 
while the Apple CD writer says the disk cannot be modified.

I do not understand what is going on.

Thanks.