Unrelated to the output you're receiving, but this line can never be false:

if (Day_of_Week($year, $month, $day) || "1,2,3,4") {
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Also, these two lines are a little perplexing:

$nextday      = $day1.$month.$year;
$nextday      = (length($day1) < 2) ? "0".$day1."." :$day1;
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The second assignment clobbers the first one... may as well just get rid of the first one.

At any rate, can you post the exact code that's failing, and the exact copied and pasted output? I still don't think we've seen code, and output from the same version of your script.