[CentOS] Problems with writing Dual Layer DVD

Hi,

I am running Centos 4 (fully updated on this box).

I removed the old DVD writer (/dev/hdc) and installed a new LG GH20 
"Internal Super Multi DVD Rewriter" with a SATA interface - this shows 
up as /dev/scd0.

When I insert a pre-recorded DVD autorun mounts it and displays the 
contents without any hassles. It appears to me that the required kernel 
modules are loaded - as copied below from lsmod output.

sata_nv                18629  0
libata                111261  1 sata_nv
sd_mod                 17217  0
scsi_mod              125261  3 sr_mod,libata,sd_mod

I am using Verbatim DVD-RDL blanks.

When I try to write a pre-recorded iso to the DVD I get the following 
error message:

[user at test]$ growisofs -dvd-compat -Z /dev/dvdwriter=<pre-recorded>.iso
:-( /dev/dvdwriter: media is not recognized as recordable DVD: 10015

I have tried to do this as root with the same result. /dev/dvdwriter is 
a link to /dev/scd0 and has full read/write/execute permissions.

Output of growisofs -version:

* growisofs by <appro at fy.chalmers.se>, version 5.21,
  front-ending to mkisofs: mkisofs 2.01 (i686-pc-linux-gnu)

Any suggestions will be welcome - if any further information is required 
I will do my best to supply it.

I have Googled with the error message but only get reports of this 
problem and no solutions.

TIA

ChrisG