Error happened when opening connection to the remote host. This includes impossibility to connect, forceful closing of socket after connection and SSL/TLS handshake failure.
Communication failed for unidentified reason during sending request or retrieving response.
The provided URL has invalid protocol identifier (i.e. not HTTP and not HTTPS).
The response header contains unparseable date/time values. This error is handled internally so you should not normally see it.
Error reported by compression engine when trying to decompress incoming data or when trying to compress outgoing data.
Digest or NTLM authentication failed.
Note that this error is reported only when something goes wrong during performing this particular authentication types.
For regular HTTPS authentication error is reported by the server via 401 response code.
Response headers could not be parsed by the client for whatever reason (usually due to malformed response).
Client request headers could not be parsed by the server for whatever reason (usually due to malformed request).