diff --git a/hio/bin/t06.c b/hio/bin/t06.c
index 5054233..35ce920 100644
--- a/hio/bin/t06.c
+++ b/hio/bin/t06.c
@@ -387,6 +387,7 @@ static int try_to_accept (hio_dev_sck_t* sck, hio_dev_sck_qxmsg_t* qxmsg, int in
 	g_htts_no = (g_htts_no + 1) % g_num_thrs;
 	pthread_mutex_unlock (&g_htts_mutex);
 
+	/* 0: index to the QX socket device (see the the first binding address to hi_svc_htts_start) */
 	if (hio_svc_htts_writetosidechan(htts, 0, qxmsg, HIO_SIZEOF(*qxmsg)) <= -1)
 	{
 		hio_bch_t buf[128];
@@ -414,7 +415,7 @@ static int try_to_accept (hio_dev_sck_t* sck, hio_dev_sck_qxmsg_t* qxmsg, int in
 		else
 		{
 		sidechan_write_error:
-printf ("sidechannel write error %s\n", strerror(errno));
+//printf ("sidechannel write error errno=%d strerror=%s\n", errno, strerror(errno));
 			hio_skadtobcstr (hio, &qxmsg->remoteaddr, buf, HIO_COUNTOF(buf), HIO_SKAD_TO_BCSTR_ADDR | HIO_SKAD_TO_BCSTR_PORT); 
 			HIO_INFO2 (hio, "unable to handle the accepted connection %ld from %hs\n", (long int)qxmsg->syshnd, buf);
 
diff --git a/hio/lib/http-svr.c b/hio/lib/http-svr.c
index f5a33ac..e8495e3 100644
--- a/hio/lib/http-svr.c
+++ b/hio/lib/http-svr.c
@@ -26,6 +26,7 @@
 
 #include "http-prv.h"
 #include <hio-path.h>
+#include <errno.h>
 
 #define INVALID_LIDX HIO_TYPE_MAX(hio_oow_t)
 
@@ -389,6 +390,7 @@ hio_svc_htts_t* hio_svc_htts_start (hio_t* hio, hio_dev_sck_bind_t* binds, hio_o
 
 			default:
 				/* ignore this */
+				HIO_DEBUG3 (hio, "HTTS(%p) - [%zu] unsupported bind address type %d\n", htts, i, (int)hio_skad_family(&binds[i].localaddr));
 				continue;
 		}
 		info.m.options = HIO_DEV_SCK_MAKE_LENIENT;
@@ -417,7 +419,7 @@ hio_svc_htts_t* hio_svc_htts_start (hio_t* hio, hio_dev_sck_bind_t* binds, hio_o
 				{
 					hio_bch_t tmpbuf[HIO_SKAD_IP_STRLEN + 1];
 					hio_skadtobcstr(hio, &binds[i].localaddr, tmpbuf, HIO_COUNTOF(tmpbuf), HIO_SKAD_TO_BCSTR_ADDR | HIO_SKAD_TO_BCSTR_PORT);
-					HIO_DEBUG3 (hio, "HTTS(%p) - [%zd] unable to bind to %hs\n", htts, i, tmpbuf);
+					HIO_DEBUG3 (hio, "HTTS(%p) - [%zu] unable to bind to %hs\n", htts, i, tmpbuf);
 				}
 
 				hio_dev_sck_kill (sck);
@@ -433,7 +435,7 @@ hio_svc_htts_t* hio_svc_htts_start (hio_t* hio, hio_dev_sck_bind_t* binds, hio_o
 				{
 					hio_bch_t tmpbuf[HIO_SKAD_IP_STRLEN + 1];
 					hio_skadtobcstr(hio, &binds[i].localaddr, tmpbuf, HIO_COUNTOF(tmpbuf), HIO_SKAD_TO_BCSTR_ADDR | HIO_SKAD_TO_BCSTR_PORT);
-					HIO_DEBUG3 (hio, "HTTS(%p) - [%zd] unable to bind to %hs\n", htts, i, tmpbuf);
+					HIO_DEBUG3 (hio, "HTTS(%p) - [%zu] unable to bind to %hs\n", htts, i, tmpbuf);
 				}
 
 				hio_dev_sck_kill (sck);
@@ -447,7 +449,7 @@ hio_svc_htts_t* hio_svc_htts_start (hio_t* hio, hio_dev_sck_bind_t* binds, hio_o
 			hio_bch_t tmpbuf[HIO_SKAD_IP_STRLEN + 1];
 			hio_dev_sck_getsockaddr(sck, &tmpad);
 			hio_skadtobcstr(hio, &tmpad, tmpbuf, HIO_COUNTOF(tmpbuf), HIO_SKAD_TO_BCSTR_ADDR | HIO_SKAD_TO_BCSTR_PORT);
-			HIO_DEBUG3 (hio, "HTTS(%p) - [%zd] listening on %hs\n", htts, i, tmpbuf);
+			HIO_DEBUG3 (hio, "HTTS(%p) - [%zu] listening on %hs\n", htts, i, tmpbuf);
 		}
 
 		htts->l.sck[i] = sck;
@@ -681,13 +683,17 @@ int hio_svc_htts_writetosidechan (hio_svc_htts_t* htts, hio_oow_t idx, const voi
 {
 	if (idx >= htts->l.count)
 	{
-		hio_seterrbfmt (htts->hio, HIO_EINVAL, "index out of range");
+		/* don't set the error information - TODO: change hio_seterrbfmt thread-safe?
+		 *hio_seterrbfmt (htts->hio, HIO_EINVAL, "index out of range");*/ 
+		errno = EINVAL;
 		return -1;
 	}
 
 	if (!htts->l.sck[idx])
 	{
-		hio_seterrbfmt (htts->hio, HIO_EINVAL, "no listener at the given index");
+		/* don't set the error information 
+		 *hio_seterrbfmt (htts->hio, HIO_EINVAL, "no listener at the given index"); */
+		errno = EINVAL;
 		return -1;
 	}
 
diff --git a/hio/lib/sck.c b/hio/lib/sck.c
index 76819e2..c875e64 100644
--- a/hio/lib/sck.c
+++ b/hio/lib/sck.c
@@ -2532,7 +2532,12 @@ int hio_dev_sck_sendfileok (hio_dev_sck_t* dev)
 
 int hio_dev_sck_writetosidechan (hio_dev_sck_t* dev, const void* dptr, hio_oow_t dlen)
 {
-	if (write(dev->side_chan, dptr, dlen) <= -1) return -1; /* this doesn't set the error information. if you may check errno, though */
+	if (write(dev->side_chan, dptr, dlen) <= -1) 
+	{
+		/* this doesn't set the error information on the main socket. if you may check errno, though */
+		/* TODO: make hio_seterrbfmt() thread safe and set the error information properly. still the caller may be in the thread-unsafe context */
+		return -1; 
+	}
 	return 0;
 }