Cd not alwd ni

I have a Rowe CD100E. Recently I started getting the CD not alwd ni message when I would pick some CDs. All have been initialized, they used to work, then sporadically, I would get the message. Restarting the machine would help, sometimes moving the problem to other discs, leaving the old discs back to being selected.
Just put in a CD Adapter and hard drive. Everything was fine, but now it's doing the same thing. Seems to be at random on random discs. Now that the CD player is completely out of the picture, what is the next troubleshooting step?

I think you are gonna-hafta, deal with Mr. Grumpy, at CD adaptor on this one--
( His real name is Ed Fisher, and he's really a nice guy--but for sure, call him that once, and he will get the opportunity {as long as his wife is not there} to say something "nasty", about me--- don't tell him I admitted that !)
Good luck--let us know the answer on this--
Ron Rich