On Tue, 10 Aug 2010, Allin Cottrell wrote: OK, I see where that message is coming from, and gretl is so confused by your mixed-up command that it's hard to see how we could produce a better message ;-) By specifying --restrict you are telling gretl to use a boolean condition, which in effect means a temporary series which has a zero or non-zero value at each observation. In this case the formula for that series is "1974:01 1974:12". Gretl begins by recognizing "1974:01" as an observation label that, in this dataset, translates to obs 13, hence the "13". But then it finds a second integer, separated by a space, and the only interpretation it can place on this is that you want to create a list, the first element of which is variable number 13. You get the same error message if you do series s = 1974:01 1974:12 But I'll think a bit more about how we might trigger an error before we get so confused. Allin Cottrell