Iīve a dubt. When I choose in Gretl: Model->Time series-> Autoregressive estimation, if I try estimating the model without constant, Gretl tells me "Error in data", but if I include the constant it makes the estimation correctly, why does it occurs? is it a bug, isn't it? 
On the other hand, if I select copy output, the estimated coefficients donīt be pasted while the rest of output is pasted (for example in word),