Jetpack sharing not working for Google and Facebook

Since last September I am no longer able to automaticly post my articles via publicize neither on facebook nor on google+. I have tried all the tricks like reconnecting to wordpress.com, disabling all plugins, deleting cache, and so on. Even all possible combinations.
At first I had the problem with facebook, google+ worked. When I tried to reactivate facebook, I tried to disconnect from google+ as well. Since that, also google+ cannot be connectet.

The error code thrown is: -32601

This seems to be an xmlrpc error, but I am not sure.

When I try to access:
https://thomas.flying-bordercollies.de/xmlrpc.php

I get the correct result:

XML-RPC server accepts POST requests only.

When I try to access:

https://thomas.flying-bordercollies.de/xmlrpc.php?rsd

I get the correct(?) result:

`<rsd xmlns=”https://archipelago.phrasewise.com/rsd&#8221; version=”1.0″>
<service>
<engineName>WordPress</engineName>
<engineLink>https://www.ads-software.com/</engineLink&gt;
<homePageLink>https://thomas.flying-bordercollies.de</homePageLink&gt;
<apis>
<api name=”WordPress” blogID=”1″ preferred=”true” apiLink=”https://thomas.flying-bordercollies.de/xmlrpc.php”/&gt;
<api name=”Movable Type” blogID=”1″ preferred=”false” apiLink=”https://thomas.flying-bordercollies.de/xmlrpc.php”/&gt;
<api name=”MetaWeblog” blogID=”1″ preferred=”false” apiLink=”https://thomas.flying-bordercollies.de/xmlrpc.php”/&gt;
<api name=”Blogger” blogID=”1″ preferred=”false” apiLink=”https://thomas.flying-bordercollies.de/xmlrpc.php”/&gt;
</apis>
</service>
</rsd>`

Also tested with http instead of https…just to be sure…

BUT when I check the Jetpack Debug-Info link ist says:

SELF:
	Array
(
    [headers] => Array
        (
            [server] => nginx
            [date] => Mon, 27 Apr 2015 09:28:44 GMT
            [content-type] => text/plain;charset=utf-8
            [connection] => close
            [x-pingback] => https://jetpack.wordpress.com/xmlrpc.php
            [expires] => Wed, 11 Jan 1984 05:00:00 GMT
            [cache-control] => no-cache, must-revalidate, max-age=60
            [pragma] => no-cache
            [x-hacker] => Jetpack Test
        )

    [body] => {"error":"Communication error","error_description":"We were unable to make an XML-RPC request to your website. Please make sure that XML-RPC is turned on and that Jetpack is installed, activated and connected with your WordPress.com account. If the error persists, try disconnecting and connecting Jetpack again."}
    [response] => Array
        (
            [code] => 400
            [message] => Bad Request
        )

    [cookies] => Array
        (
        )

    [filename] =>
)

The site is hostet at one.com, support says cURL is available and turned on. It is in a subfolder all alone, no other things inside there. What could be my Problem? I think it is not a problem with Facebook or Google+ as both throw the same error code.

Link to the affected blog: https://thomas.flying-bordercollies.de