Binos, are you sure your dual-layer blank disk is DVD-R? I just bought a couple of spindles of Verbatim dual-layer and they only come in DVD+R. in fact, I haven't been able to source any DVD-R dual-layer blanks anywhere. (I always use DVD-R single-layer disks, have burnt over a thousand now).
If your burner software is up-to-date, it should immediately let you know it can't burn the blank due to format incompatibility.