> If I try a Verbatim DVD+RW, I get the following:
> :-[ LBA=0h, SENSE KEY=5h/ASC=30h/ASCQ=10h ] -[ media is not formatted or
> :unsupported ] -( write failed: Input/output error

This sounds like you need to use
dvd+rw-format
prior to any write attempt.

About Memorex: Check your drives media list. For some drives a firmware
upgrade is needed in order to use some media types. (If you are lucky,
your drive manufacturer provides DOS usable flash utility...) This would
be especially true for 4x media in 2x drive and similar cases (not only
this one though).