error in generating script from VU Generator

hi,
I am able to record script in VU Gen(using Web(click and script)), but unable to replay it, while replaying its showing error as
Error -26547: Authentication required, please use web_set_user, e.g. web_set_user("domain\\user", "password", "host:port"); [MsgId: MERR-26547]

can anyone please tell me the reason, and how i can fix it.
i also tried to give username password and host port in vuser_init, but still unable to fix it.