Kctan,
Your problem sounds familiar.. With mine, symptoms were at times my Verdi would just read the sacds, and on another, quite the reversal--reading only red books. Error or toc kept appearing when playing the sacds, then finally '0' on the display. Might just be a case of bad optic (wear and tear). Had mine replaced 3x in the span of 6yrs. More likely to happen if you do not use the unit much or through humidity or so I was told.
Purchased from dCS the whole optical assy (parts only) costs 450 pounds (3-4yrs ago). In fact it's a Sony unit they are using, so for my 2nd and 3rd replacements I sourced them direct from a local Sony authorized and had my technician friend do it. All up it cost me around U$D100--so quite a saving there. Parts code are : Device, Optical KHM-230AAA, SCD-333ES, Sony. Hope this helps.