Web_Set_User - Why Am I Seeing This?

I am getting an error of -26547: Authentication required, please use web_set_user, e.g. web_set_user("domain\\user", "password", "host:port"); 

First, why am I getting this?

Second, what am I supposed to login with?

Third, how can I find what the host and port are?

Can I avoid this error?

VuGen 12.01

IE11