jangly mark

I hope someone can help me with this. When I put a disc into my machine, I am continually getting "Disc Error" flashing on the screen. The machine then ejects the disc. It started doing this with a handful of discs months ago, but, is now doing it with over half the discs I have. When I do manage to record, it is struggling to play the disc back. Has anyone got any ideas what is wrong? The one thought that occured to me was that it may be the lens (I smoke). Would that cause the problems I'm getting? If so (or otherwise), how would I go about fixing the problem? My machine is a MDS JE-510. janglymark (at) yahoo (dot) co (dot) uk