URL monitoring problem - basic authentication

I try to use url monitor with basic authentication ( https - ssl channel ). However, I get the following error message:

Resource down.
The resource https://sample.com/abc.htm is not available. The request requires user authentication. The response MUST include a WWW-Authenticate header field (section 14.47) containing a challenge applicable to the requested resource. The client MAY repeat the request with a suitable Authorization header field (section 14.8). If the request already included Authorization credentials, then the 401 response indicates that authorization has been refused for those credentials. If the 401 response contains the same challenge as the prior response, and the user agent has already attempted authentication at least once, then the user SHOULD be presented the entity that was given in the response, since that entity might include relevant diagnostic information. ";: ResponseCode - 401

Please help. What's wrong? Thanks at all.