Rick's guide book indicated that you could reserve a seat on the train portion of the Bernina Express (Tirano to St Moritz). When we went to the reservations site we were able to book a seat on the bus portion but the site said we could not book a train seat. any information about this discrepancy? many thanks in advance.
which reservations site were you using?
Were you trying for one of the expensive tourist trains or one of the hourly local trains which ply this route every hour?
How far ahead of your travel are trying to make reservations? 1st Class or 2nd Class? How many people?
The Rhaetischebahn website is a little tricky. If you are traveling on a rail pass and just need to book the reservation. Search recent threads and how to do it was described in just the last week or two.
When you get to the payment page, select "Ticket Available" to signify that you already have a ticket and just want the reservation.