Hi mac289 and welcome to cdfreaks,
If you're bkups are failing consistently near the end, I'd say you're burning too close to the edge, given the media you're using. Philips is pretty marginal to crappy media. I'd reduce your target size to 4300 and pick up some better quality media; hard to go wrong with verbatim and Taiyo Yuden. You may be all set once you change to quality media. A lot of us are set to burn to 4472.
You can obtain the MID (media code) of your blanks with Nero CD-DVD Speed (just click on the link).
As you burn out toward the edge of the disc, the dye tends to thin out, wobble increases, the laser has greater difficulty focusing, etc., etc. This is true of all media, but the predisposition to errors is much greater with lousy media.
For some great info about media, take a look at: