i think the memorex DVD+R media are only usable in newer cd/dvd drives thats the thing..
if u use the memorex in an intel imac they will seem to work fine... but they are really flimsy
+ cheap and easily damaged..
i think they are incompatible with older drives from 10 years ago.. there has been changes in standards regarding dvd media since 2007/2008 the dvd consortium has allowed the DVD+R standard in, and other changes they made to allow companies to make media a bit differently.. at least thats what i read.. some brands keep their media produced in the older tried + true methods + materials.. thats the only explanation i can think of.
also check this
http://www.diffen.com/difference/DVD%2BR_vs_DVD-Rlists the companies on either side of the "+" or "-" media types
the "-" type was originally backed by the companies: Apple, Pioneer , Mitsubishi, Hitachi (the latter 3 being the original leaders of the whole optical media industry pretty much!!)
u should buy some of those plastic cd sleeves they sell now if u are at a computer store.. they are really cheap + are really handy for taking care of your disks and making sure they dont get scratched!! plus u can fit 2 cds in on either side of the sleeve jackets so u can pair multiple cds together easily etc
hope it works out for you!! ive been using only verbatim the last few months and have had no problems since dumping memorex.. memorex is crap when it comes to compatibility with these older drives..
u could always replace the drive completely with a SATA CD/DVD drive with a sata to IDE adapter such as this:
http://mediagate.pbworks.com/f/1240855949/SATA_to_ATA_IDE_Converter_Adapter_%281%29.jpg then u would know that the drive supports DVD+R properly .. any drive from 2008+ should support DVD+R media but the older drives, they sometimes work, sometimes not...
similarly i have a 2006 toshiba A100 Satellite laptop..it has a MATSHITA UJ-841S DVD-RAM drive and it cant read really old CD-R's!!! just a few weeks ago i had to plug in a really ancient 1998 or 1999 CD-R drive to a desktop pc to be able to copy some akai format sample cds that i created back in the late 90s... my laptop would not read the disks.. it would say that the discs were empty/blank if inserted and prompted me to burn stuff on them, but putting the discs into a really ancient MATSUSHITA cd-r drive (4x??) it read them and i was able to image the disks to .iso files !