Since SmartConnect uses the WinHTTP by Microsoft here is a provisional list of errorcodes:
ERROR_WINHTTP_AUTO_PROXY_SERVICE_ERROR
12178 Returned by WinHttpGetProxyForUrl when a proxy for the specified URL cannot be located.
ERROR_WINHTTP_AUTODETECTION_FAILED
12180 Returned by WinHttpDetectAutoProxyConfigUrl if WinHTTP was unable to discover the URL of the Proxy Auto-Configuration (PAC) file.
ERROR_WINHTTP_BAD_AUTO_PROXY_SCRIPT
12166 An error occurred executing the script code in the Proxy Auto-Configuration (PAC) file.
ERROR_WINHTTP_CANNOT_CALL_AFTER_OPEN
12103 Returned by the HttpRequest object if a specified option cannot be requested after the Open method has been called.
ERROR_WINHTTP_CANNOT_CALL_AFTER_SEND
12102 Returned by the HttpRequest object if a requested operation cannot be performed after calling the Send method.
ERROR_WINHTTP_CANNOT_CALL_BEFORE_OPEN
12100 Returned by the HttpRequest object if a requested operation cannot be performed before calling the Open method.
ERROR_WINHTTP_CANNOT_CALL_BEFORE_SEND
12101 Returned by the HttpRequest object if a requested operation cannot be performed before calling the Send method.
ERROR_WINHTTP_CANNOT_CONNECT
12029 Returned if connection to the server failed.
ERROR_WINHTTP_CLIENT_AUTH_CERT_NEEDED
The server requires SSL client Authentication. The application retrieves the list of certificate issuers by calling WinHttpQueryOption with the WINHTTP_OPTION_CLIENT_CERT_ISSUER_LIST option. For more information, see the WINHTTP_OPTION_CLIENT_CERT_ISSUER_LIST option. If the server requests the client certificate, but does not require it, the application can alternately call WinHttpSetOption with the WINHTTP_OPTION_CLIENT_CERT_CONTEXT option. In this case, the application specifies the WINHTTP_NO_CLIENT_CERT_CONTEXT macro in the lpBuffer parameter of WinHttpSetOption. For more information, see the WINHTTP_OPTION_CLIENT_CERT_CONTEXT option. Windows Server 2003 with SP1 and Windows XP with SP2: This error is not supported.
ERROR_WINHTTP_CLIENT_CERT_NO_ACCESS_PRIVATE_KEY
The application does not have the required privileges to access the private key associated with the client certificate. Windows Server 2003 with SP1 and Windows XP with SP2: This error is not supported.
ERROR_WINHTTP_CLIENT_CERT_NO_PRIVATE_KEY
The context for the SSL client certificate does not have a private key associated with it. The client certificate may have been imported to the computer without the private key. Windows Server 2003 with SP1 and Windows XP with SP2: This error is not supported.
ERROR_WINHTTP_CHUNKED_ENCODING_HEADER_SIZE_OVERFLOW
12183 Returned by WinHttpReceiveResponse when an overflow condition is encountered in the course of parsing chunked encoding.
ERROR_WINHTTP_CLIENT_AUTH_CERT_NEEDED
12044 Returned by WinHttpReceiveResponse when the server requests client authentication. Windows Server 2003 with SP1 and Windows XP with SP2: This error is not supported.
ERROR_WINHTTP_CONNECTION_ERROR
12030 The connection with the server has been reset or terminated, or an incompatible SSL protocol was encountered. For example, WinHTTP version 5.1 does not support SSL2 unless the client specifically enables it.
ERROR_WINHTTP_HEADER_ALREADY_EXISTS
12155 Obsolete; no longer used.
ERROR_WINHTTP_HEADER_COUNT_EXCEEDED
12181 Returned by WinHttpReceiveResponse when a larger number of headers were present in a response than WinHTTP could receive.
ERROR_WINHTTP_HEADER_NOT_FOUND
12150 The requested header cannot be located.
ERROR_WINHTTP_HEADER_SIZE_OVERFLOW
12182 Returned by WinHttpReceiveResponse when the size of headers received exceeds the limit for the request handle.
ERROR_WINHTTP_INCORRECT_HANDLE_STATE
12019 The requested operation cannot be carried out because the handle supplied is not in the correct state.
ERROR_WINHTTP_INCORRECT_HANDLE_TYPE
12018 The type of handle supplied is incorrect for this operation.
ERROR_WINHTTP_INTERNAL_ERROR
12004 An internal error has occurred.
ERROR_WINHTTP_INVALID_OPTION
12009 A request to WinHttpQueryOption or WinHttpSetOption specified an invalid option value.
ERROR_WINHTTP_INVALID_QUERY_REQUEST
12154 Obsolete; no longer used.
ERROR_WINHTTP_INVALID_SERVER_RESPONSE
12152 The server response cannot be parsed.
ERROR_WINHTTP_INVALID_URL
12005 The URL is not valid.
ERROR_WINHTTP_LOGIN_FAILURE
12015 The login attempt failed. When this error is encountered, the request handle should be closed with WinHttpCloseHandle. A new request handle must be created before retrying the function that originally produced this error.
ERROR_WINHTTP_NAME_NOT_RESOLVED
12007 The server name cannot be resolved.
ERROR_WINHTTP_NOT_INITIALIZED
12172 Obsolete; no longer used.
ERROR_WINHTTP_OPERATION_CANCELLED
12017 The operation was canceled, usually because the handle on which the request was operating was closed before the operation completed.
ERROR_WINHTTP_OPTION_NOT_SETTABLE
12011 The requested option cannot be set, only queried.
ERROR_WINHTTP_OUT_OF_HANDLES
12001 Obsolete; no longer used.
ERROR_WINHTTP_REDIRECT_FAILED
12156 The redirection failed because either the scheme changed or all attempts made to redirect failed (default is five attempts).
ERROR_WINHTTP_RESEND_REQUEST
12032 The WinHTTP function failed. The desired function can be retried on the same request handle.
ERROR_WINHTTP_RESPONSE_DRAIN_OVERFLOW
12184 Returned when an incoming response exceeds an internal WinHTTP size limit.
ERROR_WINHTTP_SECURE_CERT_CN_INVALID
12038 Returned when a certificate CN name does not match the passed value (equivalent to a CERT_E_CN_NO_MATCH error).
ERROR_WINHTTP_SECURE_CERT_DATE_INVALID
12037 Indicates that a required certificate is not within its validity period when verifying against the current system clock or the timestamp in the signed file, or that the validity periods of the certification chain do not nest correctly (equivalent to a CERT_E_EXPIRED or a CERT_E_VALIDITYPERIODNESTING error).
ERROR_WINHTTP_SECURE_CERT_REV_FAILED
12057 Indicates that revocation cannot be checked because the revocation server was offline (equivalent to CRYPT_E_REVOCATION_OFFLINE).
ERROR_WINHTTP_SECURE_CERT_REVOKED
12170 Indicates that a certificate has been revoked (equivalent to CRYPT_E_REVOKED).
ERROR_WINHTTP_SECURE_CERT_WRONG_USAGE
12179 Indicates that a certificate is not valid for the requested usage (equivalent to CERT_E_WRONG_USAGE).
ERROR_WINHTTP_SECURE_CHANNEL_ERROR
12157 Indicates that an error occurred having to do with a secure channel (equivalent to error codes that begin with "SEC_E_" and "SEC_I_" listed in the "winerror.h" header file).
ERROR_WINHTTP_SECURE_FAILURE
12175 One or more errors were found in the Secure Sockets Layer (SSL) certificate sent by the server. To determine what type of error was encountered, check for a WINHTTP_CALLBACK_STATUS_SECURE_FAILURE notification in a status callback function. For more information, see WINHTTP_STATUS_CALLBACK.
ERROR_WINHTTP_SECURE_INVALID_CA
12045 Indicates that a certificate chain was processed, but terminated in a root certificate that is not trusted by the trust provider (equivalent to CERT_E_UNTRUSTEDROOT).
ERROR_WINHTTP_SECURE_INVALID_CERT
12169 Indicates that a certificate is invalid (equivalent to errors such as CERT_E_ROLE, CERT_E_PATHLENCONST, CERT_E_CRITICAL, CERT_E_PURPOSE, CERT_E_ISSUERCHAINING, CERT_E_MALFORMED and CERT_E_CHAINING).
ERROR_WINHTTP_SHUTDOWN
12012 The WinHTTP function support is being shut down or unloaded.
ERROR_WINHTTP_TIMEOUT
12002 The request has timed out.
ERROR_WINHTTP_UNABLE_TO_DOWNLOAD_SCRIPT
12167 The PAC file cannot be downloaded. For example, the server referenced by the PAC URL may not have been reachable, or the server returned a 404 NOT FOUND response.
ERROR_WINHTTP_UNRECOGNIZED_SCHEME
12006 The URL specified a scheme other than "http:" or "https:".
ERROR_NOT_ENOUGH_MEMORY
Not enough memory was available to complete the requested operation. Header: Declared in Winerror.h
ERROR_INSUFFICIENT_BUFFER
The size, in bytes, of the buffer supplied to a function was insufficient to contain the returned data. For more information, see the specific function. Header: Declared in Winerror.h
ERROR_INVALID_HANDLE
The handle passed to the application programming interface (API) has been either invalidated or closed. Header: Declared in Winerror.h
ERROR_NO_MORE_FILES
No more files have been found. Header: Declared in Winerror.h
ERROR_NO_MORE_ITEMS
No more items have been found. Header: Declared in Winerror.h
ERROR_NOT_SUPPORTED
The required protocol stack is not loaded and the application cannot start WinSock. Header: Declared in Winerror.h