"unsucessful burn. insufficient media memory"

My project is only 2615mb in size. I'm using std 4.70Gb DVD+R discs
All plays back in preview, with no issues
I'm using a HP Z8000 pavilion, Pentium 4, 3.ooGHz with XP Home Edition v2002 SP3 and 2.00 GB RAM, and burning to a USB 2.0 external Sony Optiarc AD-7201A DVD/CD writer.
There appears to be ample media memory 2.6GB to 4.7GB disc, I'm assuming its referring to the DVD+R discs, although I could be completely wrong!!
Is my system under powered for the project?