[Limdep Nlogit List] wtp in lclogit

[RAUX Charles]

Hello,
I have a specification of latent class multinomial model (below)

lclogit; choices=air, car, bus, train, none
               ; lhs=choicem
               ; model: U(air, car, bus, train) = <asca, ascc, 0, asct>
                              + <da, dc, db, dt> * duration + pc * price
                              / U(none) = anone
               ; show model
               ; pds=6; pts=2
               ; wtp=da/pc, dc/pc, db/pc, dt/pc$

This works fine, parameters are significant and the matrix wtpi is created with four columns and nearly 300 rows (the individuals). But filled only with zero. What is wrong?
Charles Raux