I have 811 which is slightly older version of 851. I found that Memorex DVD-RW disc does not work with it. Other brands I used work such as Imation.
By the way, how did you write it. Do you use it the same way as DVD-R or do you use it as "a big/huge floppy"? If it is the 2nd way, you need packet writting software to format it first.