So all of my DVD+RW discs are useless for my MacMini

I was fustrated the fact that the MacMini with Toast Premium software couldn't create a proper OSX Lion Preview DVD (I right clicked on the .dmg file and select "Toast It") when I used those DVD+RW disc that I brought and used 3+ years ago.  But when I finally used a DVD+R disc, everything went well.  Obviously MacMini hates my old DVD+RW disc.

At least it finally worked.

Also, copying .dmg (3+ Gb) across my home network doesn't seem to work. It's so much better if I just copy over the rar pieces and then decompress them on my Mac.