31-12-1969 is the day prior to the Unix Epoch (January 1 1970). You got an error some place. If all you need is day month and year why use strftime? Also, what is the value of $a1[llogin] ? To use strftime I think you you need $a1[llogin] to evaluate to a timestamp.
Try something along the lines of
date("d-m-Y", strtotime($a1[llogin]))
assuming $a1[llogin] is valid
Don