IIS and ARR to reverse proxy returns 502.3

09:55:41.903 ::>>>> WinHttp Version 6.0 Build 6.1.7601 >>>>Process w3wp.exe [12784 (0x31f0)] started at 09:55:41.903 12/20/2013
09:55:41.903 ::WinHttpSetOption(0x0, WINHTTP_OPTION_WORKER_THREAD_COUNT (80), 0xa0ec20 [0xc], 4)
09:55:41.903 ::WinHttpSetOption() returning TRUE
09:55:41.904 ::WinHttpOpen("", WINHTTP_ACCESS_TYPE_NO_PROXY (1), "", "", 0x10000000)
09:55:41.904 ::winhttp-dll added a reference to winhttp.dll (via LoadLibrary() call)
09:55:41.905 ::thread-pool created
09:55:41.905 ::thread pool initialized successfully
09:55:41.905 ::_SvcsStartup() succeeded; async-count = 1
09:55:41.905 ::WinHttpOpen() returning handle 0x1401a50
09:55:41.905 ::WinHttpSetStatusCallback(0x1401a50, 0xd6125514, 0x17e0000)
09:55:41.905 ::WinHttpSetStatusCallback() returning NULL
09:55:41.905 ::WinHttpSetOption(0x1401a50, WINHTTP_OPTION_REDIRECT_POLICY (88), 0xa0ebc0 [0x0], 4)
09:55:41.905 ::WinHttpSetOption() returning TRUE
09:55:53.277 ::WinHttpConnect(0x1401a50, "www.mysite.com", 81, 0x0)
09:55:53.277 ::Indicate Status 0x14a5930, 0x0, WINHTTP_CALLBACK_STATUS_HANDLE_CREATED (1024), 0x1f8d6a8 [0x14a5930], 8
09:55:53.277 ::WinHttpConnect() returning handle 0x14a5930
09:55:53.277 ::WinHttpOpenRequest(0x14a5930, "GET", "/new-page", "HTTP/1.1", "", 0x0, 0x00000080)
09:55:53.277 ::Indicate Status 0x290eb20, 0x0, WINHTTP_CALLBACK_STATUS_HANDLE_CREATED (1024), 0x1f8d638 [0x290eb20], 8
09:55:53.277 ::WinHttpCreateUrl(0x1f8d570, 0x0, 0x0, 0x1f8d638)
09:55:53.277 ::    WinHttpCreateUrl(); URL = (null), URL Length = 0
09:55:53.277 ::    WinHttpCreateUrl: error 122 [ERROR_INSUFFICIENT_BUFFER]
09:55:53.277 ::WinHttpCreateUrl() returning FALSE
09:55:53.277 ::WinHttpCreateUrl(0x1f8d570, 0x0, 0x14aadd0, 0x1f8d638)
09:55:53.277 ::    WinHttpCreateUrl(); URL = http://www.mysite.com:81/new-page, URL Length = 45
09:55:53.277 ::WinHttpCreateUrl() returning TRUE
09:55:53.277 ::WinHttpOpenRequest() returning handle 0x290eb20
09:55:53.277 ::WinHttpSetTimeouts(0x290eb20, 120000, 120000, 120000, 120000)
09:55:53.277 ::WinHttpSetTimeouts() returning TRUE
09:55:53.277 ::WinHttpSetOption(0x290eb20, WINHTTP_OPTION_MAX_RESPONSE_DRAIN_SIZE (92), 0x1f8d84c [0x400000], 4)
09:55:53.277 ::WinHttpSetOption() returning TRUE
09:55:53.277 ::WinHttpSetOption(0x290eb20, WINHTTP_OPTION_MAX_RESPONSE_HEADER_SIZE (91), 0x1f8d850 [0x10000], 4)
09:55:53.277 ::WinHttpSetOption() returning TRUE
09:55:53.277 ::WinHttpSetOption(0x290eb20, WINHTTP_OPTION_DISABLE_FEATURE (63), 0x1f8d840 [0x5], 4)
09:55:53.277 ::WinHttpSetOption() returning TRUE
09:55:53.278 ::WinHttpSendRequest(0x290eb20, "Cache-Control: max-age=0\r\nAccept: text/html,application/xhtml+xml,application/xm", 1062, 0x0, 0, 0, 290e8b0)
09:55:53.278 ::WinHttpAddRequestHeaders(0x290eb20, "Cache-Control: max-age=0\r\nAccept: text/html,application/xhtml+xml,application/xm", 1062, 0x20000000)
09:55:53.278 ::WinHttpAddRequestHeaders() returning TRUE
09:55:53.278 ::usr-req 0290EEA0 transitioning from state _READY to state _SENDING_RECVING
09:55:53.278 ::sys-req updates BytesToSend to 0
09:55:53.278 ::sys-req transitioning from state _INIT to state _SENDING
09:55:53.278 ::current thread is not impersonating
09:55:53.278 ::sys-sender calling HttpSendHttpRequest(overlapped = 02905460)
09:55:53.278 ::sys-sender transitioning from state  _INIT to state  _SENDING
09:55:53.279 ::usr-req 0290EEA0 received OnDnsResolvingName callback
09:55:53.279 ::sys-req pends send-request
09:55:53.279 ::WinHttpSendRequest() returning TRUE
09:55:53.279 ::usr-req 0290EEA0 received OnDnsNameResolved callback
09:55:53.280 ::usr-req 0290EEA0 received OnTcpConnecting callback
09:55:53.284 ::usr-req 0290EEA0 received OnTcpConnected callback
09:55:53.284 ::usr-req 0290EEA0 received OnSendingRequest callback
09:55:53.285 ::usr-req 0290EEA0 received OnRequestSent callback
09:55:57.078 ::  <c-b> an async I/O operation completes (overlapped = 02905460, #bytes/info = 0, error = ERROR_SUCCESS (0))
09:55:57.078 ::sys-sender processing HttpSendHttpRequest completion (error-cdoe = ERROR_SUCCESS (0x0), #bytes = 0, overlapped = 02905460)
09:55:57.079 ::sys-sender sent a request successfully
09:55:57.079 ::sys-req completing a send-request call (error = ERROR_SUCCESS (0))
09:55:57.079 ::usr-req 0290EEA0 received OnSendRequest callback; error = ERROR_SUCCESS (0)
09:55:57.079 ::Completing WinHttpSendRequest() with success; Request Handle = 0290EB20, Context = 0290E8B0, Buffer = 00000000 (0x0), Buffer Length = 0
09:55:57.079 ::WinHttpReceiveResponse(0x290eb20, 0x0)
09:55:57.079 ::sys-recver starts in _INIT state
09:55:57.079 ::current thread is not impersonating
09:55:57.079 ::sys-recver processing WebReceiveHttpResponse completion (error-cdoe = ERROR_BAD_NET_RESP (0x3a), overlapped = 02905460))
09:55:57.079 ::sys-recver failed to receive headers; error = ERROR_BAD_NET_RESP (58)
09:55:57.079 ::ERROR_WINHTTP_FROM_WIN32 mapped (ERROR_BAD_NET_RESP) 58 to (ERROR_HTTP_INVALID_SERVER_RESPONSE) 12152
09:55:57.079 ::sys-recver returning ERROR_HTTP_INVALID_SERVER_RESPONSE (12152) from RecvResponse()
09:55:57.079 ::sys-req shutting down; recv-headers encountered fatal error; error = ERROR_HTTP_INVALID_SERVER_RESPONSE (12152)
09:55:57.079 ::sys-req completes recv-headers inline (sync); error = ERROR_HTTP_INVALID_SERVER_RESPONSE (12152)
09:55:57.079 ::usr-req 0290EEA0 releases sys-req 01483180
09:55:57.079 ::sys-req failed to cancel the request; the object is already shutting down
09:55:57.079 ::Completing WinHttpReceiveResponse() with error ERROR_HTTP_INVALID_SERVER_RESPONSE (12152); Request Handle = 0290EB20, Context = 0290E8B0
09:55:57.079 ::WinHttpReceiveResponse() returning TRUE
09:55:57.081 ::WinHttpCloseHandle(0x290eb20)
09:55:57.081 ::usr-req 0290EEA0 is shutting down
09:55:57.081 ::Indicate Status 0x290eb20, 0x290e8b0, WINHTTP_CALLBACK_STATUS_HANDLE_CLOSING (2048), 0x1f8f760 [0x290eb20], 8
09:55:57.081 ::WinHttpCloseHandle() returning TRUE