Just a quick note:

Some discs have been known to reject DVD2ONE and DVD SHRINK, two of the most popular "shrinking" programs to convert a DVD9 to a DVD 5 (recordable DVD size, single layer).

DVD Rebuilder (freeware), with either the QuEnc or FreeEnc encoders (also freeware), has been know to shrink discs rejected by others.

A guide for this is forthcoming in January, but I thought it was worth a quick mention in the support forum.