Cannot submit the word in the textarea

Cannot submit the word in the textarea

I have a problem. when i write the word <script src=""></script> in the
textarea and submit to display the text, my web server doesn't allow to do
that. But i tested it with another web server it worked well. Can you tell
me what is the main problem? is it related to web server? how to deal with
it? here is the simple code I tested.
<form action="test.php" method="post">
<textarea name="txt"></textarea>
<input type="submit" name="btn" />
</form>
test.php
<?php
$text=$_POST['txt'];
echo htmlspecialchars($text);
?>