WSAEISCONN (10056)
Socket is already connected
A connect request was made on an already connected socket. Some implementations also return this error if sendto is called on a connected SOCK_DGRAM socket (For SOCK_STREAM sockets, the "to" parameter in sendto is ignored), although other implementations treat this as a legal occurrence.

WSAENOTCONN (10057)
Socket is not connected
A request to send or receive data was disallowed because the socket is not connected and (when sending on a datagram socket using sendto) no address was supplied. Any other type of operation might also return this error - for example, setsockoptsetting SO_KEEPALIVE if the connection has been reset.

WSAESHUTDOWN (10058)
Cannot send after socket shutdown
A request to send or receive data was disallowed because the socket had already been shut down in that direction with a previous shutdown call. By calling shutdown a partial close of a socket is requested, which is a signal that sending or receiving or both has been discontinued.

WSAETIMEDOUT (10060)
Connection timed out
A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.

WSAECONNREFUSED (10061)
Connection refused
No connection could be made because the target machine actively refused it. This usually results from trying to connect to a service that is inactive on the foreign host— i.e. one with no server application running.

WSAEHOSTDOWN (10064)
Host is down
A socket operation failed because the destination host was down. A socket operation encountered a dead host. Networking activity on the local host has not been initiated. These conditions are more likely to be indicated by the error WSAETIMEDOUT

WSAEHOSTUNREACH (10065)
No route to host
A socket operation was attempted to an unreachable host. This error also occurs when your ISP is intentionally blocking port 25 (the SMTP port) in an attempt to reduce spamming through their systems. See WSAENETUNREACH 10051

WSAEPROCLIM (10067)
Too many processes
A Windows Sockets implementation may have a limit on the number of applications that may use it simultaneously. WSAStartup may fail with this error if the limit has been reached.

WSASYSNOTREADY (10091)
Network subsystem is unavailable
This error is returned by WSAStartup if the Windows Sockets implementation cannot function at this time because the underlying system it uses to provide network services is currently unavailable. Users should check:

• that the WINSOCK.DLL file is in the current path,
   
• that the WINSOCK.DLL file is from the same vendor as the underlying protocol stack. They cannot be mixed and matched (WinSock DLLs must be supplied by the same vendor that provided the underlying protocol stack).
   
• that they are not trying to use more than one Windows Sockets implementation simultaneously. If there is more than one WINSOCK DLL on your system, be sure the first one in the path is appropriate for the network subsystem currently loaded.
   
• the Windows Sockets implementation documentation to be sure all necessary components are currently installed and configured correctly.

WSAVERNOTSUPPORTED (10092)
WINSOCK.DLL version out of range
The current Windows Sockets implementation does not support the Windows Sockets specification version requested by the application. Check that no old WINSOCK.DLL files are being accessed, or contact the stack vendor to see if an updated WINSOCK.DLL exists.

WSANOTINITIALISED (10093)
Successful WSAStartup not yet performed
Either the application hasn't called WSAStartup or WSAStartup failed. The application may be accessing a socket which the current active task does not own (i.e. trying to share a socket between tasks), or WSACleanup has been called too many times.

WSAEDISCON (10094)
Graceful shutdown in progress
Returned by recv, WSARecvto indicate the remote party has initiated a graceful shutdown sequence.

WSAHOST_NOT_FOUND (11001)
Host not found
No such host is known. The name is not an official hostname or alias, or it cannot be found in the database(s) being queried. This error may also be returned for protocol and service queries, and means the specified name could not be found in the relevant database.

WSATRY_AGAIN (11002)
Non-authoritative host not found
This is usually a temporary error during hostname resolution and means that the local server did not receive a response from an authoritative server. A retry at some time later may be successful.

WSANO_RECOVERY (11003)
This is a non-recoverable error
This indicates some sort of non-recoverable error occurred during a database lookup. This may be because the database files (e.g. BSD-compatible HOSTS, SERVICES or PROTOCOLS files) could not be found, or a DNS request was returned by the server with a severe error.

WSANO_DATA (11004)
Valid name, no data record of requested type
The requested name is valid and was found in the database, but it does not have the correct associated data being resolved for. The usual example for this is a hostname -> address translation attempt (using gethostbyname or WSAAsyncGetHostByName) which uses the DNS (Domain Name Server), and an MX record is returned but no A record - indicating the host itself exists, but is not directly reachable.

WSA_INVALID_HANDLE (OS dependent)
Specified event object handle is invalid
An application attempts to use an event object, but the specified handle is not valid.

WSA_INVALID_PARAMETER (OS dependent)
One or more parameters are invalid
An application used a Windows Sockets function which directly maps to a Win32 function. The Win32 function is indicating a problem with one or more parameters.

WSAINVALIDPROCTABLE (OS dependent)
Invalid procedure table from service provider
A service provider returned a bogus proc table to WS2_32.DLL. (Usually caused by one or more of the function pointers being NULL.)

WSAINVALIDPROVIDER (OS dependent)
Invalid service provider version number
A service provider returned a version number other than 2.0.

WSA_IO_PENDING (OS dependent)
Overlapped operations will complete later
The application has initiated an overlapped operation which cannot be completed immediately. A completion indication will be given at a later time when the operation has been completed.

WSA_IO_INCOMPLETE (OS dependent)
Overlapped I/O event object not in signaled state
The application has tried to determine the status of an overlapped operation which is not yet completed. Applications that use WSAWaitForMultipleEvents in a polling mode to determine when an overlapped operation has completed will get this error code until the operation is complete.

WSA_NOT_ENOUGH_MEMORY (OS dependent)
Insufficient memory available
An application used a Windows Sockets function which directly maps to a Win32 function. The Win32 function is indicating a lack of required memory resources.

WSAPROVIDERFAILEDINIT (OS dependent)
Unable to initialize a service provider
Either a service provider's DLL could not be loaded (LoadLibrary failed) or the provider's WSPStartup/NSPStartupfunction failed.

WSASYSCALLFAILURE (OS dependent)
System call failure
Returned when a system call that should never fail does. For example, if a call to WaitForMultipleObjects fails or one of the registry functions fails trying to manipulate the protocol/namespace catalogs.

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