I'm new in using Gretl, and I have a problem. I have imported a database in CSV format, and get it opened without a problem. But when I open "add" from the main bar, the command "first differences  in selected variables" are not operational (disabled?). I need first differences because I have encountered colinearity. Also, when I run a OLS regression, the results of the Durbin-Watson are not shown. This not happens when I am using a "sample file". Can you help me, please? Un saludo Adolfo