Trying to get property of non-object in /wp-includes/nav-menu.php on line 592 ??

Hi, im running wordpress 3.4.2 and

I currently ran into this problem:
I added a second wp_nav_menu(); in my header; to create a mobile phone menu. Everything works fine in the visual side, but when i turn on

define(‘WP_DEBUG_LOG’, true);
define(‘WP_DEBUG_DISPLAY’, true);

I get PHP notices:
[19-Nov-2012 09:05:10 UTC] PHP Notice: Trying to get property of non-object in /var/www/wp-includes/nav-menu.php on line 592

On my Apache2 Error log, there are even Errors which overload my log files -.-

When I google this problem with this string;

Trying to get property of non-object in /wp-includes/nav-menu.php on line 592

it seems to be a common problem; but nobody wants / needs to fix it ?

https://www.google.at/search?q=Trying+to+get+property+of+non-object+in+%2Fvar%2Fwww%2Fdemo.icsl.at%2Fwp-includes%2Fnav-menu.php+on+line+592&rlz=1C1LENP_enAT491AT491&oq=Trying+to+get+property+of+non-object+in+%2Fvar%2Fwww%2Fdemo.icsl.at%2Fwp-includes%2Fnav-menu.php+on+line+592&aqs=chrome.0.57.161&sugexp=chrome,mod=1&sourceid=chrome&ie=UTF-8#q=Trying+to+get+property+of+non-object+in+/wp-includes/nav-menu.php+on+line+592&hl=de&rlz=1C1LENP_enAT491AT491&prmd=imvns&ei=ovWpUJDuMcnKsgaGtoG4BQ&start=20&sa=N&bav=on.2,or.r_gc.r_pw.r_cp.r_qf.&fp=192604aeddc23e14&bpcl=38625945&biw=1920&bih=1038

So however, I could nail the problem down to my call to
wp_nav_menu( array(
‘container’ => ”,
‘menu_class’ => ‘tinymenu’,
‘echo’ => true,
‘before’ => ”,
‘after’ => ”,
‘link_before’ => ”,
‘link_after’ => ”,
‘depth’ => 0,
‘exclude’ => ‘290, 293, 282, 286’,
‘walker’ => new Roots_Nav_Walker())
);
But even without any parameters (only wp_nav_menu) leads to this PHP notice, and I want to fix it, because it burries me.

Hope you can help me.

with kind regards