Thank you so much Andrew for your replay.
You can check out my edmx model from this link: https://dl.dropbox.com/u/6660682/model.edmx
I change my InsertHistoryOperation method as yours. I noticed that the Generate method with a byte[] argument, return an hexadecimal string. I suppose that this is working very well for SQLServer but is it the same for Postgres?
Cheers,
Darionato