Dirty Disk Problem with DVD+R Disks on SONY RDR-GX300?

I'm having lots of "dirty disk" problems when I try to record on DVD+R
disks in my SONY RDR-GX300.  The ones giving me a problem are Memorex
(both 4x and 8x speeds) and CompUSA (4x speed) generic brands.

Any information or advice to help me with this problem?  I have had
absolutely no problems recording on DVD-R or DVD+RW disks -- not even
one failure in dozens of recordings.  (I have not tried DVD-RW, so I
have no experience with that format.)

I would just avoid using DVD+R disks for recording, but I got a bunch
of them as a gift and want to use them up if possible.
Thanks.

Goodler
SEVEN OUT OF TWENTY +RW DISKS FROM MEMOREX WILL NOT FORMAT-(DIRTY DISK)
Have the RDR-GX300 recorder. I get frequent "dirty disc" and "cannot play this disc" messages. Sometimes wiping the disk with a soft cloth works, but lately nothing works. Brand new discs get a little into the formatting and the error messages start. It's about 2 1/2 years old and it was not cheap. My cheap Wal-Mart machine is more dependable.