There are two ways of making burnatonce support DVD writing.
1. Use the official cdrecord-ProDVD version and check the readme for the key.
2. Use a patched cdrecord build with DVD support (OSS DVD extensions).
For the second option here are the instructions :
Download a patched build of cdrecord v2.01.01a06 + cygwin1.dll :
http://www.paehl.com/open_source/?download=cdrdvd_oss.zipCopy cdrecord.exe + cygwin1.dll to your burnatonce\external directory and rename cdrecord.exe to prodvd.exe.