PHP Warning

Hello everyone, I have a problem!
This is my first post here, hope it is well written.

My problem
I opened my error_log today, that is inside the public_html folder and this is what i saw:

[25-May-2012 13:50:12] PHP Warning:  call_user_func_array() [<a href='function.call-user-func-array'>function.call-user-func-array</a>]: First argument is expected to be a valid callback, 'wp_admin_bar_wp_menu' was given in /***/wp-includes/plugin.php on line 486
[25-May-2012 13:50:12] PHP Warning:  call_user_func_array() [<a href='function.call-user-func-array'>function.call-user-func-array</a>]: First argument is expected to be a valid callback, 'wp_admin_bar_comments_menu' was given in /***/wp-includes/plugin.php on line 486

***: edited out

Line 486 of plugin.php is:

do {
		foreach( (array) current($wp_filter[$tag]) as $the_ )
			if ( !is_null($the_['function']) )
				call_user_func_array($the_['function'], array_slice($args, 0, (int) $the_['accepted_args']));

	} while ( next($wp_filter[$tag]) !== false );

	array_pop($wp_current_filter);
}

My plugins folder:

• aksimet
• contact-form-7
• contact-form-7-widget
• lightbox-plus
• resize-at-upload
• simple-admin-menu-editor
• wp-table-reloaded

\

My theme is skeleton: http://demos.simplethemes.com/skeleton/

Is this error slowing my wordpress down?
Hope someone has a clue or advice, will be very appreciated, thanks.