Fatal error: Call to undefined function: array_diff_key() in /path/to/my/drupal/ in line 80

ugly but working workaround: (needed to make it work fast)
adding this function (mentioned on http://php.net/manual/de/function.array-diff-key.php, by contact-at-autonoma-dot-fr) in file /sites/all/modules/admin/admin.admin.inc

function php4_array_diff_key( )
{
$arrs = func_get_args();
$result = array_shift($arrs);
foreach ($arrs as $array) {
foreach ($result as $key => $v) {
if (array_key_exists($key, $array)) {
unset($result[$key]);
}
}
}
return $result;
}

...

and replacing the call to array_diff_key in line 80 (and code around) with this:

#
# heavy changes
#

if( function_exists( array_diff_key )) {
foreach (array_diff_key($block_info, $options) as $bid => $info) {
$module = array_shift(explode('-', $bid));
$module = isset($modules[$module]) ? $modules[$module] : $module;
$custom_options[$module][$bid] = $info['info'];
}
}
else
{
foreach( php4_array_diff_key( $block_info, $options ) as $bid => $info ) {
$module = array_shift( explode('-', $bid));
$module = isset($modules[$module]) ? $modules[$module] : $module;
$custom_options[$module][$bid] = $info['info'];
}
}

#
#
#

tested, works for me.