Usually, the conflicts between Adobe programs and DVD burners revolve around packet-writing software, like Roxio and Nero.
Normally, many Adobe programs, that can write to DVD can co-exist perfectly, with no conflicts. Many people have PrPro2.0, and a couple of versions of Encore on the same machine with no problems (PrPro 2.0 was the last version to also write to DVD, and later versions only did it through the respective versions of Encore). Now, I do not know about multiple versions of PE causing any problems. Someone, who has done that will have to comment. Still, it seems highly unlikely. Still, this is a situation, about which I know nothing.
PE7 is not an upgrade as such but a full program, it will not remove PE3 when you install it. You need manually to remove PE3. However they can "live" together on the same PC. I suppose PE3 could be "hogging" your DVD drive, if you no longer need PE3 you could try removing it.
By the way, can you burn to folder with PE7?
All problems seem to have gone away after much detective work. Even though I had previously deleted Roxio Creator and the Sonic programs, when I examined the registry I found remnants of their existence remaining. These entries in the registry were carefully removed, and after a reboot, PE7 was operating without problems.
I became aware of this possibility after carefully searching the forum ... heed the advice posted frequently on this forum bout third part DVD burner SW.
Thanks for everyone's help.
That is good news. As you, and many others, have found out, some other burning programs can spread out tentacles all over the system and these are not easy to remove. All Adobe programs, that Burn to DVD need 100% control of the burners, and many programs hook the burners at boot-up.