Quote by Nurlan:

my browser is IE6,
I`m upgrade my forum to 1.5.2 version,
When users click on "New thread" (also on "quote" and "reply") browser is inform about syntax error.
Same I observe in this forum too.

I want attach the screenshot, but this function is not work too.

And my small suggestion:
for correct display in any languages, it is necessary to replace in line 1581 of cp.inc.php  

<small>(Format: T.M.J)</small>

with this

<small>' . $T['search_date_format'] . '</small>

Quote by Yves:

Quick fix: in file post.inc.php, function is_valid_attach_name, replace
    $ext = substr($filename, $x);
with
    $ext = substr($filename, $x + 1);
This makes the specified list of allowed attachment filename extensions work again.

Quote by Yves:

What syntax error? My browser doesn't do that. Maybe you can describe what you can see on your display?

Quote by Yves:

Ah yes. As I said, I always forget something... I found and fixed the bug. Thank you for that note.

Changed post.inc.php line 1916 from
    echo '<script type="text/javascript"><![CDATA[' . endl;
into
    echo '<script type="text/javascript">//<![CDATA[' . endl;