POST xml > "invalid Parameter!" response

[Th3Br0]

Hi guys, im just strugle around with some xml POST request and always getting a "invalid Parameter!" response.
Thats what i want to do:

POST DATA (Standart, text/plain, only Encode Content deselected):

<v:Envelope xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns:d="http://www.w3.org/2001/XMLSchema" xmlns:c="http://schemas.xmlsoap.org/soap/encoding/" xmlns:v="http://schemas.xmlsoap.org/soap/envelope/"><v:Header /><v:Body><n0:getSiteList id="o0" c:root="1" xmlns:n0="urn:WebServices"><vCountry i:type="d:string">en</vCountry></n0:getSiteList></v:Body></v:Envelope>

When i post this im always getting this response:

<?xml version="1.0" encoding="UTF-8"?><SOAP-ENV:Envelope SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/"><SOAP-ENV:Body><LoginCustomerResponse><return xsi:type="xsd:string">{&quot;message&quot;:&quot;invalid Parameter!&quot;}</return></LoginCustomerResponse></SOAP-ENV:Body></SOAP-ENV:Envelope>

Im debugging it and the response should not contain invalid Parameter, do you have any ideas for this?

Thank you very much!