</form> not valid!?

Hello, I'm Roberto and I'm italian.
My site is valid, but if I add at the end of any form this: "</form>" the validator shows me an error.. Why? It is a bug?

Here you can find the html code.
http://pastebin.com/m20e10b0

The error is at line 90.

<form method="post" action="search.php" />
                                Keyword:<br />
                                <input type="text" name="keyword"
value="" class="tx" style="width: 120px;" /><br />
                                <input type="submit" value="Cerca"
class="submit" />
                        </form>

Bye