apex soap 1.2 call out

Question

I am trying to do http callout with soap 1.2 request but facing following error..?

Error - System.UnexpectedException: java.lang.IllegalArgumentException: invalid start or end.

request:-

HttpRequest req = new HttpRequest();
req.setMethod('POST');
req.setHeader('Accept-Encoding','gzip,deflate');
req.setHeader('Content-Type','text/xml;charset=UTF-8;action=\"MRBDirectUploads_v1_Binder_ping\"');
req.setHeader('User-Agent','xxx');
req.setHeader('Host', 'bfs-webservices-test.macquarie.com.au');
req.setHeader('Content-Length','xxx');
req.setEndpoint('https://bfs-webservices-test.macquarie.com.au/bfs/b2b/ws/MRBDirectUploads:v1/MRBDirectUploads_v1_Port');

req.setBody(header);          
HTTPResponse res =new HttpResponse();
Http http = new Http();
system.debug('request' +res+'#Header' );
res = http.send(req);