it's a good idea to add a cd-burners group if you are planning to write cds with your normal user account.
try burning your CDs as root user or do a
chown root:root /usr/local/bin/cdrecord
chmod u+s /usr/local/bin/cdrecord
to run cdrecord in suid-root-mode.
if this doesn't help check how you created
the iso-images for the 2nd, ..., n-th session:
you have to use cdrecord's switch "-msinfo" to retrieve information about the sessions already on CD. See manpages on cdrecord and mkisofs an the cd-writing-howto.