I have bought three versions of Roxio EMC: v4, 6 & 9. When trying to read old UDF CDs made with v4 or 6 (I do nor remember), I cannot see the files, but de UDF setup icon, and XP does not permit it to run whet starting up the computer, because it can damage the environment. I bought V9 because of those CDs I haven't use for a while. How can I recover my files?.

They really should be readable but I have seen them refused. It took a reboot and the old discs were then readable by XP's built in Reader. (you do not want to install an old non-XP Reader)

I cannot speak for V4 but I could read V5 and V6 on XP but it did take a little persistence…

The older discs will not be writable in V9 but discs formatted by V9 D2D will be writable back to V6.

It is possible that they have gone bad. Packet writers were never intended for any sort of backup. They are useful as a way to transfer data between PC's where no other means exists.