HELP! Error during parsing input XMLProtocolMessage

I'm getting this error when I try to send over data using a remote call: /// get Amazon Proxy handle $amazon = getAmazonSOAP(true); /// try to create a soap attachment attached to the filename $v = new SOAP_Attachment('attachedDocument', 'text/plain', $filename); $merchant = new Merchant($merchantToken, $merchantName); /// try to pass the $value object as the payload for the transport $resp = $amazon->postDocument($merchant->__to_soap(), '_POST_INVENTORY_AVAILABILITY_DATA_', $v); --- now, I know that I am connecting to amazon's wsdl and everything, but it returns this error: SOAP-ENV:Client Error during parsing input XMLProtocolMessage WASP_XMLTokenizerException [WASP_XPP_XmlPullParserException]: only whitespace content allowed outside root element at line 6 and column 3 I think that I am encoding the data wrong, because it must be seeing it as improperly formatted XML. How do I fix that ? I've tried setting the Content-Type to everything i could think of "application/octet-stream", "text/plain", "text/xml", and a few others. Ive tried commenting out base64 encoding in Base.php and Value.php. I don't know where to go from here. Thanks for help!