sony burns rw's fine but not r's

[sunchaser]

hi guys,
i've only burned a few disks since i got this burner.

its a sony dw-u10a and it burns + and - disks, r and rw.

i've burned a few +rw disks making backups and testing out my dvd authoring. I finally made a dvd that i want to mass produce and when i tried to burn it onto dvd-r's my program froze. i was using dvd decrypter to burn the iso. i tried three times, and got three ruined disks. the burning just stops a few minutes into it and decrypter stays open, looking like its working, but its frozen.

i tried reburning my +rw with the iso and it worked fine. why would this multiformat burner work fine with +rw and then not at all with
-r?

thanks for any advice.
max