It sounds like the date field you are getting sometimes does not match the pattern you are expecting.

For example, if the date was 2/8/2006 1:14:42 PM, then $amonth would be undef and --$amonth would render -1; hence the error message.

Also, your supplied code snippet is wrong, you are naming the day number as $ayear and the year as $aday.

You need to verify that the date is in the format you are expecting, and perhaps allow for some alternate formats.

Maybe something like (untested):

my $app_time;
if( 
    my( $aday, $amonth, $ayear, $ahour, $amin, $asec ) = 
        $appdate =~ m[
             (\d{1,2}) [-/] (\d{1,2}) [-/] (\d{4}) \s+
             (\d{1,2})  :   (\d{1,2})  :   (\d{1,2})
        ]x
) {
    $app_time = timelocal( $asec, $amin, $ahour, $aday, --$amonth, $ay
+ear );
}
else {
    die "Invalid date (format) '$app_date'";
}
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Or you could look into using one of the many date modules from cpan.

The format for $app_date that you give appears to be month-day-year (or day-month-year—I can't tell which), but your code thinks it's year-month-day. I think your second line down should be:

($amonth,$aday,$ayear) = split(/-/, $adate);

Pulling those fields out of your input might be a little more readable with regular expressions. You could replace all of your split lines with this (unless you need $adate or $atime later):

( $amonth, $aday, $ayear, $ahour, $amin, $asec )
    = ( $app_date =~ /^(\d\d?)-(\d\d?)-(\d{4}) (1?\d):(\d\d):(\d\d)/ )
+;
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Or this, if you're into xms regexes:

( $amonth, $aday, $ayear, $ahour, $amin, $asec )
    = ( $app_date =~ m{ \A                      # beginning of string
                        (\d\d?)-(\d\d?)-(\d{4}) # month-day-year
                        \s                      # space separator
                        (1?\d):(\d\d):(\d\d)    # hour:minutes:seconds
                    }xms );
[download]

I put some debug strings and the date appears as follows: adate is 2007-01-01, atime is 12:00:00 , i had the wrong format before... I will try out the above. Is the --$month right to use?

I'd use $month-1, since there's no reason to modify $month in the process. The subtraction is required since timelocal expects a 0-based month (Jan = 0).