burning data DVD with Graveman

[Norman Silverstone]

After all the advice given here I decided to try Graveman to burn my
data to DVD because I could not get GnomeBaker to work. I am using
Verbatim DVD-RW discs. I burnt 1 file to the DVD, no problem. However,
when I tried to burn another file I had a problem. A few seconds after
pressing the burn button the drive door opened and then closed and an
error message appeared 'Communication error with grawisofs'. On opening
the DVD I noticed that the first file had disappeared and the second
file was burned to the disc. 

Could someone please explain what I am doing wrong and what I need to do
to put things right.

Norman