Aldığın hata dosyadaki ascii karakterlerden olabilir,UTF8 bomsuz kaydedilmesi gerek.

Kodlarınızı kendim çalıştırdım,post edilecek verileri siz forum dışındaki bir dosyadan gösteriyorsunuz login.php ye form action kısmında /forum/ dizinini eklemelisiniz
aşağıda kodlarınızda küçük bi düzenleme yaptım.

<!-- breadcrumb, login, pm info -->
		<if condition="$show['member']">
	<div class="smallfont">
		<strong><phrase 1="$bbuserinfo[musername]" 2="/forum/member.php?$session[sessionurl]u=$bbuserinfo[userid]">$vbphrase[welcome_x_link_y]</phrase></strong><br />
		<phrase 1="$pmbox[lastvisitdate]" 2="$pmbox[lastvisittime]">$vbphrase[last_visited_x_at_y]</phrase>

		<if condition="$show['notifications']">
			<div><span id="notifications"><a href="/forum/usercp.php$session[sessionurl_q]">$vbphrase[your_notifications]:</a> <strong>$notifications_total</strong></span></div>
			<if condition="$show['popups']">
				<script type="text/javascript"> vBmenu.register("notifications"); </script>
			<else />
				<script type="text/javascript" src="/forum/clientscript/vbulletin_notifications_nopopups.js?v=$vboptions[simpleversion]"></script>
				<script type="text/javascript"> vBulletin.register_control("vB_Notifications_NoPopups", "notifications");  </script>
			</if>
		<else /><if condition="$show['pmstats']">
			<div><phrase 1="$vbphrase[unread_x_nav_compiled]" 2="$vbphrase[total_x_nav_compiled]" 3="$session[sessionurl_q]">$vbphrase[private_messages_nav]</phrase></div>
		</if></if>

		<if condition="$show['pmwarning']"><div><strong><phrase 1="$vbphrase[pmpercent_nav_compiled]">$vbphrase[your_pm_box_is_x_full]</phrase></strong></div></if>
	</div>
<else />
		<!-- login form -->
		<form action="/forum/login.php?do=login" method="post" onsubmit="md5hash(vb_login_password, vb_login_md5password, vb_login_md5password_utf, $show[nopasswordempty])">
		<script type="text/javascript" src="/forum/clientscript/vbulletin_md5.js?v=$vboptions[simpleversion]"></script>
		<label for="navbar_username">$vbphrase[username]</label>
			<input type="text" class="bginput" style="font-size: 11px" name="vb_login_username" id="navbar_username" size="10" accesskey="u" tabindex="101" value="$vbphrase[username]" onfocus="if (this.value == '$vbphrase[username]') this.value = '';" />		
			<label for="navbar_password">$vbphrase[password]</label>
			<input type="password" class="bginput" style="font-size: 11px" name="vb_login_password" id="navbar_password" size="10" tabindex="102" />
			<label for="cb_cookieuser_navbar"><input type="checkbox" name="cookieuser" value="1" tabindex="103" id="cb_cookieuser_navbar" accesskey="c" />$vbphrase[remember_me]</label>
			<input type="submit" class="button" value="$vbphrase[log_in]" tabindex="104" title="$vbphrase[enter_username_to_login_or_register]" accesskey="s" />
		
		<input type="hidden" name="s" value="$session[sessionhash]" />
		<input type="hidden" name="securitytoken" value="$bbuserinfo[securitytoken]" />
		<input type="hidden" name="do" value="login" />
		<input type="hidden" name="vb_login_md5password" />
		<input type="hidden" name="vb_login_md5password_utf" />
		</form>
		<!-- / login form -->
</if>
<!-- / breadcrumb, login, pm info -->



<br />

<if condition="$show['notices']">
<form action="/forum/profile.php?do=dismissnotice" method="post" id="notices">
<input type="hidden" name="do" value="dismissnotice" />
<input type="hidden" name="securitytoken" value="$bbuserinfo[securitytoken]" />
<input type="hidden" id="dismiss_notice_hidden" name="dismiss_noticeid" value="" />
<input type="hidden" name="url" value="$return_link" />$vbphrase[notices]
			$notices
</form>
</if>

Ayrıca bu dosyadan forum klasörüne kuracağınız her url bağlantısında (vbulletin js dosyalarını çekme gibi) /forum dizinini eklemelisiniz.