Either your drive can't see the larger discs, or you need to chance a setting in your software. If you are using NERO, put in a blank disc and check the cd-info to see how big it says the cd is. If it's an 80minute/700MB disc it should go 79:xx:xx , with xx:xx being any number. Some discs actually have nearly 80minutes of space, some only advertise they do and have somewhere between 74 and 79.
You can adjust NERO's settings to change the "too much on the disc" marker, but it's really only the cd-info that will help you. You can also use a CD ATIP software reader to check the capacity of the blanks.
--Kisai
"Hmm, I wonder how many pieces this will end up as when it hits the ground?"