Canon Pixma iP4950 not printing dvd-rs


2 brand-new CANON Pixma iP4950 printers refuse to print images on dvd-rs - keeps repeating error 1851 "inner cover is open...." (it has to be open to admit the dvd holder into the correct position).

We have been told by Canon it must be a faulty batch of printer HOWEVER our original printer (Canon Pixma iP4500) suddenly developed this very same issue (still prints off paper copies with no problem) after printing dvds over a number of years, with no problem. As above the inner cover was always open as it is designed to be in order to print dvds.

We think we have tried everything including trying out a suggested solution for an earlier model of Canon printer posted several years ago on this forum. Unfortunately hasn't worked for these models.

Has anyone experienced this problem and has a solution?
If you are not willing to accept what the manufacturer told you, then there is precious little that anyone here can do for you.