[Gretl-users] fixed effects panel estimation

Hello everybody, it may sound silly, but I simply cannot understand why when calculating fixed effects panel estimation, some variables are "omitted due to the collinearity" and the constant remains. Should not also constant disappear from the estimation - as it bears the fixed effects??? I am calculating log-gravity models and the important variables are omitted. What do I do wrong? How can I get know the coefficient of omitted variables? IT IS IMPROTANT FOR MY ESTIMATION? Thank you for your help. Iveta