Oxtender 2 - blocked by a firewall

[exchange]

Hello,
in the next weaks i will migrate from 6.14.0 Rev14 to 6.20.1 Rev5.

On my testsystem i will test the Oxtender 2. But I can't use it.

On the client i receive:

---- Sync State ----

Error during Login (SST_LOGIN)

---- Message ----

HTTP 403

---- Location ----



---- Details ----

Der Server verweigert das Erfüllen der Anforderung (HTTP 403, Forbidden).

---- Error Object ----

{
  "code": 2148369411,
  "code_hex": "0x800d8403",
  "code_description": "unknown USM error",
  "state": 2,
  "state_description": "SST_LOGIN",
  "last_usm_call": 
    {
      "func": "/usm-json/login",
      "argument": 
        {
          "user": "XXX",
          "device": "f240f0b305e8f247b17e68d9fb37671c",
          "version": "1.6.9",
          "local_time": "2012-01-31 14:03:00.865",
          "password": "****"
        },
      "reply_string": "\u003CHTML>\u003CBODY>The page you requested has been blocked by a firewall policy restriction.\u003Cp>You are not allowed to access this web page\u003C/BODY>\u003C/HTML>\r\n"
    }
}

The client is Windows XP SP3 and Outlook 2007. The server and the client firewall is disabled!

If i use the IE on http://oxneu.rkk.local/usm-json/login i received the following message:

405 HTTP method GET is not supported by this URL
[no description available]


--------------------------------------------------------------------------------

Tue, 31 January 2012 14:13:55 GMT, Open-Xchange v6.20.1-Rev5

"--access-usm on --access-olox20 on" are beeing executed on context and user.

Can anybody help me?

Thanks