Validation weird behaviour

Hi,
Im migrating my code from rails 2.0.2 to 2.3.8. I created the
structure using script/generate and copied the codes from the old
version to controller, model and views. It is working fine, but when
I try to create a new record, I face the error msg: “Field has already
been taken”. The weird thing is that the table is clean, I did
db:migrate:reset. Does anybody has a clue on whats going on with the
"validates_uniqueness_of " validator?

Thanks,

Pedro