Gdata signed request error: "Unknown authorization header"

I have a problem with Updating and Deleting events using signed requests. Inserting events works just fine. But when Updating and Deleting I receive an "Unknown authorization header" 401 error.

For ALL three operations I first generate the client like this:

$client = new Zend_Gdata_HttpClient();  
$client->setAuthSubPrivateKeyFile('certificates/gcalkey.pem', null, true);
$client->setAuthSubToken($session_token);
$gdataCal = new Zend_Gdata_Calendar($client);

To Update an event I use this:

$eventOld = $gdataCal->getCalendarEventEntry($eventUri);

$eventOld->title = $gdataCal->newTitle('NEW NAME');
try {
    $eventOld->save();
} catch (Zend_G开发者_如何学Cdata_App_Exception $e) { print_r($e); exit; }

And it gives me the "Unknown authorization header" error. But the same code, using unsigned requests, works.

Where might be the problem? I tried modifying $eventUri to both https and http, but it seems it does not have any effect.

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I've been getting this 401 error message too, creating the client and service the same way. It can retrieve a list of calendars, but fails when retrieving an event feed.

Has this worked for you before? It might not be officially supported yet.