PURE Chronos Series 2 - cd player?

As a gift I have had 2 PURE Chronos Series 2 radio / alarm / cd players. On the first machine the cd player failed, continually saying ' No Disc'.

Because it was under warranty cover I received a replacement. The cd player on the new Chronos machine has started to work intermittently. For some old cds it seems to work ok. For newer cds (that may be lighter in weight) eventually it gives the message: 'No disc'.

Any suggestions?