Sometimes you can update the firmware of the drive in the recorder and it will improve compatibility with newer types of disks that have been released since the recorder was made. I searched for a new firmware for your particular recorder and did not find one.
That leaves you with no options for these Memorex dvds. I suggest getting Verbatim brand -R disks. You can usually find them at Best Buy if you are in the US. If you want to try some RW disks, normally I would recommend Verbatim +RW, but if you are having trouble with the + variations, you can also buy Verbatim -RW.
Sony has, in the past, been a good substitute for Verbatim when the latter are not available in your area. Sony disks these days are just as unpredictable as the cruddy Memorex disks I'm afraid.
If you would like to shop online, look at stores like rima.com and supermediastore.com and buy Taiyo Yuden 8x disks. For example: http://www.rima.com/prod/1736-100.html Unfortunately it is hard to find them in less than 100 ct cakeboxes.