On Wed, 4 Apr 2012, Bulent Erdemir wrote:
 Indeed it works. Thank you very much.
 On the other, the documentation says that the format should be yyyy:mm for
 monthly date values on page 21 in User Guide. 
If dates are given as strings, then yyyy:mm is a good format 
for monthly data (though gretl will recognize a variety of 
formats).
However, your dates are not strings, they are integers (which 
represent calendar dates in Excel). If the left-most column is 
reognized as being in a standard Excel date format, then the 
date-integers will be processed correctly, but YYYY:MM is not 
a standard Excel date format so the integers are read "raw", 
in which case they don't make sense as dates.
Allin Cottrell