c++ - HTTP Posting large string fails with error code 317 -

i http posting large string of text server. string of text contents of file 800kb in size. function httpsendrequest() fails error code 317 getlasterror().

httpsendrequest(hrequest, hdrs, -1, (lpvoid)authdata.c_str(), authdata.size() * sizeof(tchar)) 

what error 317 mean? i've googled not find error means. , can i/should post such large strings (file contents) way? should use different winapi method?

edit useful info:
- server apache
- http posting php script. data not posted in query string regular posting form.
- website uses wordpress cms. know wordpress limits max upload size files. maybe wp limits http post size aswell?