While copying a big batch of files to a DVD this msj appeared: "This DVD-ROM drive is read only. You can copy files to this writable DVD but you must insert it into a writable drive".
It is a writable drive. It has written happily to DVDs before and since. The disc was a DVD-RW, and it has received files before and since.
I told it to skip files as appropriate, and it eventually finished the transfer after a fashion. Trouble is, you can't be sure it has copied all the files when this happens.
I've searched the Net and found 2 other people on other forums who have had the same msj, but no-one seems to know how to cure the problem.
So here's your chance: beat the other experts... :-)