Forms Authentication in Sharepoint 2013, _vti_bin/authentication.asmx error

Question

I'm getting this error when using CSOM in a FBA web application that is configured agains't a custom FBA provider. I'm getting this error when site is configured for Forms, if a disable forms with windows auth I can get web url. Probably would be a configuration
error if anyone can helpme...
I'm getting the error when Forms is configured: Server was unable to process request. ---> Could not retrieve the IIS Settings. Parameter name: context
Here is my CSOM code:
using (ClientContext context = new ClientContext("http://10.34.116.35:41443"))
context.AuthenticationMode = ClientAuthenticationMode.FormsAuthentication;
context.FormsAuthenticationLoginInfo = new FormsAuthenticationLoginInfo("carles", "test");
Web web = context.Web;
context.Load(web);
MessageBox.Show(web.Url);
context.Dispose();
Thanks

Answer 1

Solved,  internally CSOM calls authentication.asmx webservice if FormsAuthentication is set ... this webservice was throwing the exception... testing the web service in the server login worked against my membership... has to be a silly thing and YES
it was simply calling the api replacing the ip of the server with the host of the web application. Hope helps someone in the future.