All Error Start with 4 will be the client error....
400 - Bad request==> Routing Problem....
WCF does not return/show lot of information about what's actually wrong in its side (sad). Try configuring WCF Tracing and see if it helps.
4xx - Client Error
An error occurs, and the client appears to be at fault. For example, the client may request a page that does not exist, or the client may not provide valid authentication information.
400 - Bad request.
401 - Access denied. IIS defines several different 401 errors that indicate a more specific cause of the error. These specific error codes are displayed in the browser but are not displayed in the IIS log:
401.1 - Logon failed.
401.2 - Logon failed due to server configuration.
401.3 - Unauthorized due to ACL on resource.
401.4 - Authorization failed by filter.
401.5 - Authorization failed by ISAPI/CGI application.
401.7 - Access denied by URL authorization policy on the Web server. This error code is specific to IIS 6.0.
403 - Forbidden. IIS defines several different 403 errors that indicate a more specific cause of the error:
403.1 - Execute access forbidden.
403.2 - Read access forbidden.
403.3 - Write access forbidden.
403.4 - SSL required.
403.5 - SSL 128 required.
403.6 - IP address rejected.
403.7 - Client certificate required.
403.8 - Site access denied.
403.9 - Too many users.
403.10 - Invalid configuration.
403.11 - Password change.
403.12 - Mapper denied access.
403.13 - Client certificate revoked.
403.14 - Directory listing denied.
403.15 - Client Access Licenses exceeded.
403.16 - Client certificate is untrusted or invalid.
403.17 - Client certificate has expired or is not yet valid.
403.18 - Cannot execute requested URL in the current application pool. This error code is specific to IIS 6.0.
403.19 - Cannot execute CGIs for the client in this application pool. This error code is specific to IIS 6.0.
403.20 - Passport logon failed. This error code is specific to IIS 6.0.
404 - Not found.
404.0 - (None) - File or directory not found.
404.1 - Web site not accessible on the requested port.
404.2 - Web service extension lockdown policy prevents this request.
404.3 - MIME map policy prevents this request.
405 - HTTP verb used to access this page is not allowed (method not allowed.)
406 - Client browser does not accept the MIME type of the requested page.
407 - Proxy authentication required.
412 - Precondition failed.
413 - Request entity too large.
414 - Request-URI too long.
415 - Unsupported media type.
416 - Requested range not satisfiable.
417 - Execution failed.
423 - Locked error.Anonymus, if this helps please login to Mark As Answer. | Alert Moderator