The request failed with HTTP status 403: Forbidden
O Web Service não estabeleceu a conexão por algum problema no certificado digital da aplicação cliente. Existem diversas causas para a falha, recomendamos que o emissor tente a conexão ao Web Service pelo browser, o uso do IE é recomendado por utilizar o mesmo repositório de certificados digitais no caso de aplicações .NET, como por exemplo a biblioteca NFe_Util.dll. A conexão pelo browser mostra o código de erro HTTP com detalhes que permite identificar a real causa da falha, a seguir listamos os HTTP error da família 403 mais comuns (a lista completa está disponível em: http://www.wats.ca/show.php?contentid=36):
o HTTP Error 403.7 - certificado digital do cliente não enviado para o servidor atachado na mensagem SOAP.
Forbidden: Client certificate required. This error occurs when the resource you are attempting to access requires your browser to have a client Secure Sockets Layer (SSL) certificate that the server recognizes. This is used for authenticating you as a valid user of the resource. Please contact the Web server’s administrator to obtain a valid client certificate.
o HTTP Error 403.9 - Muitos usuários conectado - erro raro.
Access Forbidden: Too many users are connected. This error can be caused if the Web server is busy and cannot process your request due to heavy traffic. Please try to connect again later. Please contact the Web server’s administrator if the problem persists.
o HTTP Error 403.13 - O certificado do cliente se encontra revogado.
Client certificate revoked: The page you are trying to view requires the use of a valid client certificate. Your client certificate was revoked, or the revocation status could not be determined. The certificate is used for authenticating you as a valid user of the resource.
o HTTP Error 403.16 - O certificado do cliente não é confiável ou é inválido.
Client certificate untrusted or invalid: The page you are trying to view requires the use of a valid client certificate. Your client certificate is untrusted or invalid. The client certificate is used for authenticating you as a valid user of the resource.
o HTTP Error 403.17 - O certificado do cliente não se encontra no período de validade.
Client certificate has expired or is not yet valid: The page you are trying to view requires the use of a valid client certificate. Your client certificate has expired or is not yet valid. The client certificate is used for identifying you as a valid user of the resource.
Fonte: http://nf-eletronica.com/blog/?page_id=93
o HTTP Error 403.7 - certificado digital do cliente não enviado para o servidor atachado na mensagem SOAP.
Forbidden: Client certificate required. This error occurs when the resource you are attempting to access requires your browser to have a client Secure Sockets Layer (SSL) certificate that the server recognizes. This is used for authenticating you as a valid user of the resource. Please contact the Web server’s administrator to obtain a valid client certificate.
o HTTP Error 403.9 - Muitos usuários conectado - erro raro.
Access Forbidden: Too many users are connected. This error can be caused if the Web server is busy and cannot process your request due to heavy traffic. Please try to connect again later. Please contact the Web server’s administrator if the problem persists.
o HTTP Error 403.13 - O certificado do cliente se encontra revogado.
Client certificate revoked: The page you are trying to view requires the use of a valid client certificate. Your client certificate was revoked, or the revocation status could not be determined. The certificate is used for authenticating you as a valid user of the resource.
o HTTP Error 403.16 - O certificado do cliente não é confiável ou é inválido.
Client certificate untrusted or invalid: The page you are trying to view requires the use of a valid client certificate. Your client certificate is untrusted or invalid. The client certificate is used for authenticating you as a valid user of the resource.
o HTTP Error 403.17 - O certificado do cliente não se encontra no período de validade.
Client certificate has expired or is not yet valid: The page you are trying to view requires the use of a valid client certificate. Your client certificate has expired or is not yet valid. The client certificate is used for identifying you as a valid user of the resource.
Fonte: http://nf-eletronica.com/blog/?page_id=93