about post method problem

I use below codes to get post_date . when I upload a file only 512 byte , It works ok
but when I try bigger file (about 4kb) , tux says 404 not found .

	req->object_addr = (char *)malloc(req->objectlen + 1);
	memset(req->object_addr, 0, req->objectlen + 1);
	ret = tux(TUX_ACTION_READ_POST_DATA, req);
	fwrite(req->object_addr, req->objectlen, 1, OutPut);

this is log

192.168.0.210 - - Mon May  6 18:00:50 2002 "POST /demo.tux HTTP/1.1" - 0 404
192.168.0.210 - - Mon May  6 18:00:50 2002 " <none> " - 0 404

and It seems that tux even does not call my module . I've checked MAX_OBJECT_SIZE , and it looks OK (2000000000 default value).
Who can tell me how to configure tux server to get bigger file which users want to upload ?
Thanks!