Http 405 on Chrome and FF on POST WS call

Question

This is my WS :

    [HttpPost]
    [Route("api/Schema/convertDwgEnJson")]
    public IHttpActionResult Post([FromBody]FichierDwgDTO fichierDwgDTO)
    {...}

And I call it in my angular app :

var res = self.$http.post('http://localhost:52087/api/Schema/convertDwgEnJson', msgdata);

It's working with IE(11), but with chrome and FF i get a http 405 error, saying :

XMLHttpRequest cannot load http://localhost:52087/api/Schema/convertDwgEnJson. Response for preflight has invalid HTTP status code 405

What's wrong?