The exception in event viewer says:
System.Security.Authentication.AuthenticationException
at System.Net.TlsStream.EndWrite(System.IAsyncResult)
at System.Net.PooledStream.EndWrite(System.IAsyncResult)
at System.Net.ConnectStream.WriteHeadersCallback(System.IAsyncResult)
According to my knowledge, usually this is due to a certificate issue in one of your websites.