PHP warning for item in \include\functions.php

Seems like this warning appears, if the script receives data in a non-UTF encoding. We'll try to fix it.

Please, provide us the following details: the URL and the kind of request (GET or POST).

I had the same problem.

sample log

91.224.160.11 - - [16/Oct/2011:00:40:46 +0400] "GET /forum/new-reply90.html%09-%09200%094%09-%09%CA%EE%EC%EF%FC%FE%F2%E5%F0%FB%09-%09-%09-%09-%09-%09- HTTP/1.0" 404 480 "http://www.datarc.ru/forum/new-reply90.html%09-%09200%094%09-%09%CA%EE%EC%EF%FC%FE%F2%E5%F0%FB%09-%09-%09-%09-%09-%09-" "Mozilla/6.0 (compatible; MSIE 7.0a1; Windows NT 5.2; SV1)"

temporarily fixed this way, but do not think it is good way to patch functions.php directly:

function forum_htmlencode($str)
{
    $return = ($hook = get_hook('fn_forum_htmlencode_start')) ? eval($hook) : null;
    if ($return != null)
        return $return;

////    return htmlspecialchars($str, ENT_QUOTES, 'UTF-8');
    return htmlspecialchars(mb_convert_encoding($str, 'UTF-8', mb_detect_encoding($str)), ENT_QUOTES, 'UTF-8');
}

Send me link in PM that cause error.

@dimkalinux
Did you receive my PM ?

You do not need to login to trigger this error. The error is never displayed on page, only in the server logs as PHP notice:
PHP Warning:  mb_convert_encoding(): Illegal character encoding specified in ....

Changed php.ini settings to:
display_errors = On
error_reporting = E_ALL | E_STRICT | E_NOTICE | E_DEPRECATED | E_PARSE
log_errors = On
...and restarted Server, but the error is NOT displayed on page, also tried clearing browser cache and restarting browser

Please note: The mentioned error is a PHP notice only, without E_NOTICE (e.g. error_reporting = E_ALL | E_STRICT) the problem is not even logged to server log! This might be the reason why it is not displayed on page.

I already tried to make the notice displayed on page, but as mentioned in my previous post and while applying the settings you suggested, the notice is never displayed.

I certainly know how to hide error or notice messages, but I.M.O that's not the right way to solve coding issues - at least not as long you confirmed that it is a minor issue, not a security problem.

Yesterday I already tried this configuration,
I also looked at the source for hidden error messages,
and to be sure I saved and compared the pages (with and w/o error display) md5 check-sums,
they are always identical, nothing displayed.
Additionally tried to use error_prepend_string option to identify messages.

With error_reporting = E_ALL the issue is not even logged to Apache logfile!

As I mentioned in a previous topic, error_reporting = E_NOTICE is required to log the notice, but however this only logs the notice, but does not display it. Probably because display_errors will display errors and warnings only, but never notices.

Please read my previous posts more thoroughly, you always ask me for already provided information.

I do not use mb_convert_encoding !
I only tried this 5 days ago, but for a few minutes only.

BTW: Your forum log-in page features a hidden anti-spam input tag, just between the username input and the password input tags. This is a bad idea since it breaks Firefox password manager (won't remember or save log-in data).
Firefox recognizes the input above a password field as username field (even if hidden by CSS). Unfortunately this is the ant-spam honey-pot on your page which even has an autocomplete=off attribute. However, just removing this attribute won't fix the issue, you need to remove the whole input tag for the reason mentioned above. (tested and verified your source on on my own page)
I wonder why a password-protected page needs a honey-pot at all - especially the log-in page.

I'm not using the "Fancy stop spam" extension. I developed my own anti-spam PunBB extension Yasb. Meanwhile I fixed a few more Yasb bugs and I'm very happy with it. I just see you posted your intention to adopt my idea - thanks!

The reason why I mentioned the "Fancy Stop Spam" honeypot annoyance was that my Firefox does not save log-in data on http://punbb.informer.com, thus I cannot disable the honey-pot option.

Ok, I will focus on the topic now:
What's your suggestion in order to trace or resolve the "Invalid multibyte sequence in argument " issue?

You can use Xdebug extensions for PHP, but not on production server or hosting.