Hello Sascha,
I have tried to add new profile in your site, and I got this message:
<!DOCTYPE HTML PUBLIC “-//IETF//DTD HTML 2.0//EN”>
<html><head>
<title>403 Forbidden</title>
</head><body>
<h1>Forbidden</h1>
<p>You don’t have permission to access /plugins/system/jasocial_feed/admin.php
on this server.</p>
</body></html>
Our plugin use ajax to drive all action related to social profile (included add/update/remove profile actions), and the file “/plugins/system/jasocial_feed/admin.php” is used as handler for ajax request. So to resolve this issue, you need update settings of your hosting to allow access this file.