diff --git a/python/omnisocket_a_side/daemon.py b/python/omnisocket_a_side/daemon.py
index f9d9dae..e4fb251 100644
--- a/python/omnisocket_a_side/daemon.py
+++ b/python/omnisocket_a_side/daemon.py
@@ -30,9 +30,9 @@ def utc_iso_now() -> str:
 
 
 def load_omnisocket_api():
-    from omnisocket import CONTROL_DEFAULTS, MSG_TYPE_BINARY, Session, VIDEO_DEFAULTS
+    from omnisocket import CONTROL_DEFAULTS, MSG_TYPE_BINARY, MSG_TYPE_ERROR, Session, VIDEO_DEFAULTS
 
-    return CONTROL_DEFAULTS, MSG_TYPE_BINARY, Session, VIDEO_DEFAULTS
+    return CONTROL_DEFAULTS, MSG_TYPE_BINARY, MSG_TYPE_ERROR, Session, VIDEO_DEFAULTS
 
 
 def _merge_kcp_defaults(defaults: dict[str, Any], override: dict[str, Any]) -> dict[str, Any]:
@@ -50,7 +50,7 @@ def _load_config(config_path: str | None) -> dict[str, Any]:
         with path.open("r", encoding="utf-8") as file:
             raw = yaml.safe_load(file) or {}
 
-    control_defaults, _msg_type_binary, _session_cls, video_defaults = load_omnisocket_api()
+    control_defaults, _msg_type_binary, _msg_type_error, _session_cls, video_defaults = load_omnisocket_api()
 
     transport = dict(raw.get("transport", {}))
     control = dict(raw.get("control_sender", {}))
@@ -160,7 +160,7 @@ class QueuedControlEvent:
 
 class ControlSessionManager:
     def __init__(self, config: dict[str, Any]) -> None:
-        control_defaults, _msg_type_binary, session_cls, _video_defaults = load_omnisocket_api()
+        control_defaults, _msg_type_binary, _msg_type_error, session_cls, _video_defaults = load_omnisocket_api()
         transport = config["transport"]
         control_cfg = config["control_sender"]
         daemon_cfg = config["daemon"]
@@ -403,12 +403,13 @@ class ControlSessionManager:
 
 class VideoSessionManager:
     def __init__(self, config: dict[str, Any]) -> None:
-        _control_defaults, msg_type_binary, session_cls, video_defaults = load_omnisocket_api()
+        _control_defaults, msg_type_binary, msg_type_error, session_cls, video_defaults = load_omnisocket_api()
         transport = config["transport"]
         video_cfg = config["video_receiver"]
         daemon_cfg = config["daemon"]
 
         self._msg_type_binary = msg_type_binary
+        self._msg_type_error = msg_type_error
         self._session_cls = session_cls
         self._connect_kwargs = {
             "server_addr": transport["server_addr"],
@@ -517,9 +518,12 @@ class VideoSessionManager:
                     meta = session.recv_into(buffer, timeout_ms=200)
                     if meta is None:
                         continue
-                    if meta.get("msg_type") != self._msg_type_binary:
-                        continue
+                    msg_type = int(meta.get("msg_type", -1))
                     frame = bytes(buffer[: int(meta["body_len"])])
+                    if msg_type != self._msg_type_binary:
+                        self._disconnect(self._describe_unexpected_message(msg_type, frame))
+                        time.sleep(0.2)
+                        break
                     jpeg_frame = self._extract_jpeg_frame(frame)
                     if jpeg_frame is None:
                         with self._lock:
@@ -535,6 +539,14 @@ class VideoSessionManager:
                 self._disconnect(str(error))
                 time.sleep(0.2)
 
+    def _describe_unexpected_message(self, msg_type: int, payload: bytes) -> str:
+        detail = payload.decode("utf-8", errors="replace").strip()
+        if msg_type == self._msg_type_error:
+            return f"video session rejected by server: {detail or 'unknown error'}"
+        if detail:
+            return f"received unexpected video message type {msg_type}: {detail}"
+        return f"received unexpected video message type {msg_type}"
+
     def _connect(self) -> None:
         session = self._session_cls()
         try:
diff --git a/python/omnisocket_b_side/daemon.py b/python/omnisocket_b_side/daemon.py
index bd254e8..9ea9eba 100644
--- a/python/omnisocket_b_side/daemon.py
+++ b/python/omnisocket_b_side/daemon.py
@@ -39,9 +39,9 @@ def utc_iso_now() -> str:
 
 
 def load_omnisocket_api():
-    from omnisocket import CONTROL_DEFAULTS, MSG_TYPE_BINARY, Session
+    from omnisocket import CONTROL_DEFAULTS, MSG_TYPE_BINARY, MSG_TYPE_ERROR, Session
 
-    return CONTROL_DEFAULTS, MSG_TYPE_BINARY, Session
+    return CONTROL_DEFAULTS, MSG_TYPE_BINARY, MSG_TYPE_ERROR, Session
 
 
 def _merge_kcp_defaults(defaults: dict[str, Any], override: dict[str, Any]) -> dict[str, Any]:
@@ -115,7 +115,7 @@ def _load_config(config_path: str | None) -> dict[str, Any]:
         with path.open("r", encoding="utf-8") as file:
             raw = yaml.safe_load(file) or {}
 
-    control_defaults, _msg_type_binary, _session_cls = load_omnisocket_api()
+    control_defaults, _msg_type_binary, _msg_type_error, _session_cls = load_omnisocket_api()
     transport = dict(raw.get("transport", {}))
     control = dict(raw.get("control_receiver", {}))
     video = dict(raw.get("video_sender", {}))
@@ -193,12 +193,13 @@ def _load_config(config_path: str | None) -> dict[str, Any]:
 
 class ControlRecvManager:
     def __init__(self, config: dict[str, Any]) -> None:
-        control_defaults, msg_type_binary, session_cls = load_omnisocket_api()
+        control_defaults, msg_type_binary, msg_type_error, session_cls = load_omnisocket_api()
         transport = config["transport"]
         control_cfg = config["control_receiver"]
         daemon_cfg = config["daemon"]
 
         self._msg_type_binary = msg_type_binary
+        self._msg_type_error = msg_type_error
         self._session_cls = session_cls
         self._connect_kwargs = {
             "server_addr": transport["server_addr"],
@@ -307,6 +308,7 @@ class ControlRecvManager:
             if msg_type != self._msg_type_binary:
                 with self._lock:
                     self._ignored_non_binary += 1
+                self._disconnect(self._describe_unexpected_message(msg_type, payload))
                 continue
             if len(payload) != CONTROL_PACKET_STRUCT.size:
                 with self._lock:
@@ -346,6 +348,14 @@ class ControlRecvManager:
             except Exception:
                 pass
 
+    def _describe_unexpected_message(self, msg_type: int, payload: bytes) -> str:
+        detail = payload.decode("utf-8", errors="replace").strip()
+        if msg_type == self._msg_type_error:
+            return f"control session rejected by server: {detail or 'unknown error'}"
+        if detail:
+            return f"received unexpected control message type {msg_type}: {detail}"
+        return f"received unexpected control message type {msg_type}"
+
     def _enqueue_packet(self, payload: bytes) -> None:
         try:
             self._queue.put_nowait(payload)