This is what I changed to make it work with 3.5.1

Replaced:
if ($editable_statuses_array=='') $editable_statuses_array=array();

By:
if ($editable_statuses_array=='' || !is_array($editable_statuses_array)) $editable_statuses_array=array();

Then, the block:

list($count_singular_val,$dummy) = split(' ',$label_count['singular'],2);
list($count_plural_val,$dummy) = split(' ',$label_count['plural'],2);
$public_val = $status->public;
if (in_array($status->name,$editable_statuses)) {
    echo cs_print_custom_status($i, $opt_val, $slug_val, $count_singular_val, $count_plural_val, $public_val);
    $i++;
} else {
    if (('inherit'!=$status->name) && ('auto-draft'!=$status->name))
    $field .= '<p>' . $label_default . ' <input type="text" readonly="readonly" id="fixed_status_'.$slug_val .'" name="fixed_status_'.$slug_val . '" value="' . $status->label . '" size="20"></p>';
}

Needed to be wrapped with:

if (isset($label_count['singular']) && isset($label_count['plural'])) {
	// same code here
}

Bonus: in case you are using it with “Events+” plugin (by WPMUdev)
This plugin manages recurrent events, thus creates an internal statuts “recurrent” that will also populate Custom Status’ dropdown.

So I had to exclude this type from displaying in the list.
Replace line:
if ($status->name != "auto-draft" && $status->name != "inherit" ) {

By:
if ($status->name != "auto-draft" && $status->name != "inherit" && $status->name != "recurrent" ) {

That’s all for today.
Best,
Germain

https://www.ads-software.com/extend/plugins/custom-status/