Welcome to CD Freaks.
I've got the 440 and at the back of the manual it shows this error message with the following explanation and I'd guess yours is much the same:-
The disc control data limit has been reached (whatever that means) or the maximum number of chapters and/or titles has been reached. Erase titles/chapters or combine chapters.
I think you might need to delete a few titles and/or optimise the HDD.